(CNN) -- Here's a look at what you need to know about Iran's nuclear capabilities.
Since 2003, worldwide concern over Iran's nuclear program has increased as Iran and the International Atomic Energy Agency (IAEA) spar over investigation and details of Iran's program. Iran's Supreme Leader Ayatollah Khamenei has repeatedly denied Iran is building a bomb and says weapons of mass destruction are forbidden under Islam.
Timeline: 1957 - The United States signs a civil nuclear cooperation agreement with Iran.
1967 - The Tehran Nuclear Research Center, which includes a small reactor supplied by the U.S., opens.
1968 - Iran signs the Nuclear Non-Proliferation Treaty.
Mid-1970s - With U.S. backing, Iran begins developing a nuclear power program.
1979 - Iran's Islamic revolution ends Western involvement in the country's nuclear program.
December 1984 - With the aid of China, Iran opens a nuclear research center in Isfahan.
February 23, 1998 - The U.S. announces concerns that Iran's nuclear energy program could lead to the development of nuclear weapons.
March 14, 2000 - U.S. President Bill Clinton signs a law that allows sanctions against people and organizations that provide aid to Iran's nuclear program.
February 21, 2003 - IAEA Director General Mohamed ElBaradei visits Iran to survey its nuclear facilities and to encourage Iran to sign a protocol allowing IAEA inspectors greater and faster access to nuclear sites. Iran declines to sign the protocol. ElBaradei says he must accept Iran's statement that its nuclear program is for producing power and not weapons, despite U.S. claims to the contrary.
June 19, 2003 - The IAEA issues a report saying that Iran appeared to be in compliance with the Non-Proliferation Treaty, but that it needed to be more open about its activities.
August 2003 - The IAEA announces that its inspectors in Iran have found traces of highly enriched uranium at the Natanz uranium enrichment plant. Iran claims the amounts are contamination from equipment bought from other countries. Iran agrees to sign a protocol of the Nuclear Non-Proliferation treaty that allows for unannounced visits to their nuclear facilities and signs it on December 18, 2003.
October 2003 - The Foreign Ministers of Britain, France and Germany visit Tehran, and all parties agree upon measures Iran will take to settle all outstanding issues with the IAEA. Under obligation to the IAEA, Iran releases a dossier on its nuclear activities. However, the report does not contain information on where Iran acquired components for centrifuges used to enrich uranium, a fact the IAEA considers important in determining whether the uranium is to be enriched for weapons.
November 2003 - Iran agrees to halt uranium enrichment as a confidence building measure and accepts IAEA verification of suspension.
December 2003 - Iran signs an Additional Protocol with the IAEA voluntarily agreeing to broader inspections of its nuclear facilities.
February 2004 - A.Q. Khan, "father" of Pakistan's nuclear weapons program, admits to having provided Iran and other countries with uranium-enrichment equipment.
June 1, 2004 - The IAEA states they have found traces of uranium that exceed the amount used for general energy production. Iran admits that it is importing parts for advanced centrifuges that can be used to enrich uranium, but is using the parts to generate electricity. The IAEA criticizes Iran for repeatedly misstating details and making contradictory statements about its nuclear program.
July 31, 2004 - Iran states that it has resumed production on centrifuge parts used for enriching uranium, but not enrichment activities.
February 2, 2005 - Ali Agha Mohamedi, the spokesman for Iran's Supreme National Security Council, states that Iran will never end its nuclear program and that talks with EU members are merely intended to protect Iran's nuclear achievements.
August 8, 2005 - Iran restarts uranium conversion, a step on the way to enrichment, at a nuclear facility, saying it is for peaceful purposes only, and flatly rejects a European offer aimed at ensuring the nation does not seek nuclear weapons.
August 9, 2005 - Iran removes the IAEA seals from its Isfahan nuclear processing facility, opening the uranium conversion plant for full operation. IAEA spokesman Mark Gwozdecky states that the plant "is fully monitored by the IAEA" and "is not a uranium enrichment plant."
September 11, 2005 - Iran's new foreign minister, Manouchehr Mottaki, says the country won't suspend activities at its Isfahan uranium conversion facility and it plans to seek bids for the construction of two more nuclear plants.
September 17, 2005 - President Mahmoud Ahmadinejad tells the U.N. that Iran has an "inalienable right" to operate a nuclear energy program hours after Secretary of State Condoleezza Rice says Iran threatens efforts to halt nuclear proliferation.
January 10, 2006 - Iran resumes research at its Natanz uranium enrichment plant, arguing that doing so is within the terms of an agreement with the IAEA.
January 12, 2006 - Foreign ministers of the EU3 (Great Britain, France, Germany) recommend Iran's referral to the United Nations Security Council over its nuclear program.
January 13, 2006 - Iran's Foreign Minister, Manouchehr Mottaki, states that if Iran is referred, its government under law will be forced to stop some of its cooperation with the IAEA, including random inspections.
February 4, 2006 - President Ahmadinejad orders Iran to end its cooperation with the IAEA.
April 11, 2006 - Hashemi Rafsanjani, Iran's former president, states that Iran has increased the number of functioning centrifuges in its nuclear facilities in Natanz and has produced enriched uranium from them.
August 31, 2006 - The IAEA issues a report on Iran saying the Islamic republic "has not suspended its enrichment activities" despite this day's deadline to do so. Iran can possibly face economic sanctions.
December 23, 2006 - The U.N. Security Council votes unanimously to impose sanctions against Iran for failing to suspend its nuclear program.
February 22, 2007 - The IAEA issues a statement saying that Iran has not complied with U.N. Security Council for a freeze of all nuclear activity. Instead, Iran has expanded its uranium enrichment program.
March 24, 2007 - The U.N. adopts Resolution 1747 which toughens sanctions against Iran. The sanctions include the freezing of assets of 28 individuals and organizations involved in Iran's nuclear and missile programs. About a third of those are linked to the Iranian Revolutionary Guard, an elite military corps.
May 23, 2007 - The IAEA delivers its latest report to the U.N. on Iran's nuclear activities. The report states that not only has Iran failed to end its uranium enrichment program but has in fact expanded activity in that area.
June 21, 2007 - Iran's Interior Minister Mostapha PourMohamedi claims, "Now we have 3,000 centrifuges and have in our warehouses 100 kilograms of enriched uranium." ... "We also have more than 150 tons of raw materials for producing uranium gas."
December 2007 - A U.S. intelligence report finds that Iran abandoned a nuclear weapons program in 2003.
February 20, 2009 - The Institute for Science and International Security (ISIS) reports that Iranian scientists have reached "nuclear weapons breakout capability." The report concludes Iran does not yet have a nuclear weapon but does have enough low-enriched uranium for a single nuclear weapon. An official at the IAEA cautions about drawing such conclusions. The IAEA says Iran's stock of low-enriched uranium would have to be turned into highly enriched uranium (HEU) in order to be weapons-grade material.
February 25, 2009 - Iran runs tests at its Bushehr nuclear power plant using "dummy" fuel rods, loaded with lead in place of enriched uranium to simulate nuclear fuel. A news release distributed to reporters at the scene states the test measured the "pressure, temperature and flow rate" of the facility to make sure they were at appropriate levels. Officials say the next test will use enriched uranium, but it's not clear when the test will be held or when the facility will be fully operational.
September 21, 2009 - In a letter to the IAEA, Iran reveals the existence of a second nuclear facility. It is located underground at a military base, near the city of Qom.
October 25, 2009 - IAEA inspectors make their first visit to Iran's newly disclosed nuclear facility near Qom.
February 2010 - The Annual Threat Assessment presented to the Senate Intelligence Committee states, "We do not know, however, if Iran will eventually decide to build nuclear weapons."
February 18, 2010 - In a statement, the IAEA reports that it believes Iran may be working in secret to develop a nuclear warhead for a missile.
August 21, 2010 - Iran begins fueling its first nuclear energy plant, in the city of Bushehr.
December 5, 2010 - Ali Akbar Salehi, Iran's atomic chief and acting foreign minister, announces that Iran's nuclear program is self-sufficient and that Iran has begun producing yellowcake, an intermediate stage in processing uranium.
January 8, 2011 - Ali Akbar Salehi reports that Iran can now create its own nuclear fuel plates and rods.
February 25, 2011 - In a report, the IAEA raises new concerns about the intent of Iran's nuclear program, including Iran's resumed research to develop a warhead.
September 2, 2011 - An IAEA report states that Iran continues to defy U.N. sanctions aimed at curbing its nuclear program and cited increasing concerns it may be developing nuclear weapons.
September 4, 2011 - Iran announces that its Bushehr nuclear power plant joined the electric grid September 3, making it the first Middle Eastern country to produce commercial electricity from atomic reactors.
September 5, 2011 - In response to Iran's nuclear chief stating that Iran will give the IAEA "full supervision" of its nuclear program for five years if U.N. sanctions are lifted, the European Union says that Iran must first comply with international obligations.
November 8, 2011 - The IAEA releases a report saying that it has "serious concerns" and "credible" information that Iran may be developing nuclear weapons.
January 1, 2012 - The semiofficial news agency FARS says Iran succeeded in building and testing the country's first nuclear fuel rod. The rod, containing natural uranium, was successfully tested and is being "radiated in the core of the Tehran research nuclear reactor," the news agency says, citing Iran's atomic energy agency website.
January 9, 2012 - The IAEA confirms that uranium enrichment has begun at the Fordo nuclear facility in the Qom province in northern Iran.
January 23, 2012 - The European Union announces it will ban the import of Iranian crude oil and petroleum products.
January 29, 2012 - A six-member delegation from the IAEA arrives in Tehran for a three-day visit, shortly after the European Union imposes new sanctions aimed at cutting off funding to the nuclear program.
January 31, 2012 - In Senate testimony in James Clapper, Director of National Intelligence, says there's no evidence Iran is building a nuclear bomb. CIA director David Patraeus agrees.
February 15, 2012 - Iran loads the first domestically-produced nuclear fuel rods into the Tehran research reactor.
February 21, 2012 - After two days of talks in Iran about the country's nuclear program, the IAEA expresses disappointment that no progress was made and that their request to visit the Parchin military base was denied.
March 7, 2012 - The IAEA Director-General Yukiya Amano says he can't tell whether Iran's nuclear facilities and activities are for peaceful purposes. "Iran is not telling us everything that is my impression. We are asking Iran to engage with us proactively and Iran has a case to answer."
March 28, 2012 - Discussions regarding Iran's nuclear future stall.
April 14, 2012 - Talks resume between Iran and six world powers over Iranian nuclear ambitions in Istanbul, Turkey.
May 9, 2012 - Satellite imagery of the Parchin military base shows signs of increased activity, according to assessment by the ISIS. The ISIS analysis raises suspicion that Iran could be trying to clean out the facility.
May 23-24, 2012 - Iranian nuclear negotiator Saeed Jalili meets with representatives from the U.S., France, Russia, China, Great Britain and Germany, also known as P5+1, in Baghdad, Iraq. Iran is accused of "kicking the can down the road," as the group meets again on June 1.
May 25, 2012 - An IAEA report finds that environmental samples taken at the Fordo fuel enrichment plant near the city of Qom have enrichment levels of up to 27%, higher than the previous level of 20%.
June 18-19, 2012 - A meeting is held between Iran and the P5+1 (U.S., France, Russia, China, Great Britain and Germany) in Moscow. No agreement is reached.
June 28, 2012 - Saeed Jalili writes to European Union foreign policy chief Catherine Ashton warning world powers to avoid "unconstructive measures" such as the oil embargo agreed upon by the EU in January draws near.
July 1, 2012 - A full embargo of Iranian oil from the European Union takes effect.
August 30, 2012 - A United Nations report finds that Iran has stepped up its production of high-grade enriched uranium and has re-landscaped Parchin, one of its military bases, in an apparent effort to hamper a U.N. inquiry into the country's nuclear program.
April 6, 2013 - EU High Representative Catherine Ashton says that after two days of negotiations between Iran and the six world powers (the U.S., France, Britain, Germany, China and Russia), the two sides "remain far apart" on Tehran's controversial nuclear program.
April 9, 2013 - State-run TV reports that Iran opened a uranium-processing facility as well as a uranium mine in the central province of Yazd, to mark "National Nuclear Day."
September 24, 2013 - At a speech at the U.N. General Assembly Iranian President Rouhani says "Nuclear weapons and other weapons of mass destruction have no place in Iran's security and defense doctrine, and contradict our fundamental religious and ethical convictions."
October 16, 2013 - The latest discussions between Iran and the six world powers center on a proposal put forth by Iran to recognize the peaceful nature of its nuclear energy pursuits. The meeting is described as "substantive and forward-looking."
November 24, 2013 - Six world powers and Iran reach an agreement over Iran's nuclear program. The deal calls on Iran to limit its nuclear activities in return for lighter sanctions.
January 12, 2014 - It is announced that Iran will begin eliminating some of its uranium stockpile on January 20.
January 20, 2014 - Iran's nuclear spokesman Behrouz Kamalvandi tells state-run news agency IRNA that Iran has started suspending high levels of uranium enrichment.
January 20, 2014 - The European Union announces that it has suspended certain sanctions against Iran for six months. The move is part of a deal in which Iran has agreed to suspend high levels of uranium enrichment.