(CNN) -- An International Atomic Energy Agency report, dated and leaked Friday, said Iran continues to defy U.N. resolutions aimed at curbing its nuclear program and cited "increasing" concerns it may be developing nuclear weapons
The report was obtained and posted online by the Institute for Science and International Security, among other groups.
It follows a visit last month by an IAEA official to Iran, at the Middle Eastern nation's invitation. In it, the report's author notes some instances in which Iran appears to be working with the international agency, as well as conducting parts of its program as it had said it would.
But the report, intended for the IAEA's director general as well as the U.N. Security Council, also suggests Iran continues to flout U.N. and other resolutions regarding its nuclear program.
For example, "Iran has not suspended its enrichment-related activities" -- even at facilities being monitored by the IAEA, the report notes. The nation also "has not suspended work on all heavy water related projects, including the construction of the heavy water moderated research reactor."
And information that Iran may or may not be disclosing, specifically regarding possible nuclear weaponry being produced by the program, is a particularly pressing issue, according to the nine-page document.
"The agency is increasingly concerned about the possible existence in Iran of past or current undisclosed nuclear-related activities involving military-related organizations," the report states.
Specifically, it cites "new information" received by the IAEA "related to the development of a nuclear payload for a missile."
"The information available to the agency in connection with these outstanding issues is extensive and comprehensive and has been acquired both from member states and through its own efforts," the report adds.
Iran admitted to producing more than 4,500 kilograms of enriched uranium since 2007, almost enough to make four nuclear weapons, according to an ISIS analysis from David Albright, Paul Brannan, Andrea Stricker and Christina Walrond.
Iran's ambassador to the IAEA, Ali Asgshar Soltanieh, played up the report as demonstrating "the positive steps (taken by Iran) in line with cooperation and transparency," according to state-run Press TV.
"The cooperation of our country in the provision of information and clearing up ambiguities and responding to some of the questions has clearly been mentioned," Soltanieh said.
The ambassador told IRNA, another state-run news outlet, that the report has "more positive parts, compared with the past reports, and can therefore be considered a step forward."
But aside from stressing to IRNA that Iran's "nuclear activities are fully peaceful," Soltanieh did not address the program's ties to the military in his interview with either official news outlet.
Iran's nuclear program is the subject of international controversy, in light of fears expressed by the United States and other nations that Iran wants to develop nuclear weapons, an allegation Tehran has long denied. The U.N. Security Council, which is partnered with the IAEA, has imposed sanctions on Iran in an effort to curb its nuclear program.
The report states that Iran is "the only state with significant nuclear activity ... not implementing" certain IAEA provisions, and it also has not provided key information, such as its design plans for its IR-40 reactor, the report says. Tehran has vowed to answer such questions in "due time," not on the IAEA's timetable, according to the report.
"Iran is not implementing a number of its obligations," the report concludes. "Iran is not providing the necessary cooperation, (and) the agency is unable to provide a credible assurance about the absence of undeclared nuclear material and activities in Iran, and therefore to conclude that all nuclear material in Iran is in peaceful activities."
The report notes IAEA Director General Yukiya Amano met with Iranian Foreign Minister Ali Akbar Salehi and Fereydoun Abbasi, an Iranian vice president and head of its atomic energy organization, at meetings on June 21 and July 12 in Vienna, Austria.
Days after the latter meeting, the state-run IRNA news agency reported that Iran's foreign ministry said that the country is installing a new generation of centrifuges in its nuclear facilities.
At Iran's invitation, an IAEA official went to the Middle East nation in mid-August and visited several nuclear sites, including "an installation where research and development on advanced centrifuges was taking place."