BAGHDAD, Iraq (CNN) -- More than 300,000 Iraqi Shiites have signed a petition calling for an end to what they say are "Iranian terrorist interferences in Iraq" and demanding the United Nations investigate the Islamic republic's involvement in Iraq.
Iraqi Prime Minister Nuri al-Maliki, left, and Iranian President Mahmoud Ahmadinejad meet in August.
The petition seems to represent a kink in the cozy relationship between the two nations, who share the Shiite faith and whose friendliness toward each other has raised the concerns of U.S. officials.
The United States considers Iran a sponsor of terrorism and has been at the forefront of a bitter battle over Iran's nuclear program.
The U.S. suspects Iran intends to develop nuclear weapons, but Tehran says its program has only peaceful aims.
On Tuesday -- the same day Baghdad, Tehran and Washington announced a new round of talks regarding Iraqi security issues -- the Iraqi Shiite groups announced they had completed the six-month process of gathering signatures for the petition. Watch what Tehran has to say about its nuclear aspirations »
The groups demands the U.N. "dispatch a delegation to investigate the four years [of] crimes in the southern provinces by the Iranian regime and its proxies," according to a press release from the Independent National Tribal Organization in Southern Iraq.
The petition has the support of 14 members of the clergy and 600 sheiks. It also was signed by 25,000 women, the release stated.
"The most painful stab on the back of the Shiites in Iraq by the Iranian regime has been its shameful abuse of Shiite religion to achieve its ominous ends," the petition states.
The petition also is backed by the People's Mujahedeen Organization of Iran -- or Mujahedeen-e Khalq (MEK) -- which seeks to overthrow the Islamic regime in Iran.
MEK has been labeled a terrorist group by the United States, Iraq and Iran -- all for different reasons -- but it continues to operate in southern Iraq under the protection of the U.S. military despite Iraqi pressure to leave the country.
The United States considers the group a source of valuable intelligence on Iran.
Iran has blamed MEK for supporting Shiite insurgents, but MEK says "these allegations are only to cover up the crimes of the Iranian regime and its mercenaries in Iraq," according to the Shiite group's news release.
Another Iran-Iraq tiff emerged this week when Iraqi government spokesman Ali al-Dabbagh announced upcoming expert-level talks that he said will "help to establish security and stability in Iraq and to dispel the tensions in the region."
According to a report from Iran's Press TV, Iran's Foreign Ministry Spokesman Mohammad Ali Hosseini expressed concern about al-Dabbagh's characterization of the positive climate in which the talks would take place.
"Al-Dabbagh earlier said that as Iran had cut its support for insurgents in Iraq, Tehran and Washington should take advantage of the situation to hold a new round of talks," the Press TV report said. "Hosseini vehemently dismissed the accusations, calling on the Iraqi government not to be influenced by the [psychological war] waged by the U.S."
Reacting to the dust-up, al-Dabbagh's office issued a news release expressing "surprise and regret" at Hosseini's announcement.
"Al-Dabbagh said that the Iraqi government was surprised with the tense and irresponsible announcement of the spokesman for the Iranian Foreign Ministry, which he added is devoid of the customary diplomatic courtesy," the news release stated.
In the 1980s, Iran and Iraq -- then controlled by a Sunni-dominated government under Saddam Hussein -- fought a nearly decadelong war that left more than 1 million dead. The two countries have been working to improve their political and economic relationship since the U.S.-led invasion ushered in a Shiite-dominated government, but they are still divided along some cultural and political lines.
No date has been set for the expert-level talks, which will follow three previous meetings between U.S. and Iranian officials in Baghdad. But Iranian Foreign Minister Manouchehr Mottaki said another round of talks will occur in "the near future," according to the state-run Islamic Republic News Agency.
Previous rounds of talks between Iranian Ambassador Hassan Kazemi Qomi and the U.S. Ambassador to Iraq, Ryan Crocker, were held in May, July and August, hosted by the Iraqi government.
"We are open to using this channel as a way of talking directly about important issues concerning security in Iraq," State Department spokesman Sean McCormack said Tuesday.
Such U.S.-Iranian engagements were suggested by the bipartisan Iraq Study Group, which recommended U.S.-Iranian talks as a way to help improve the environment in Iraq. The Iraqi government, which is led by Shiite Muslim parties with close ties to Iran, has urged the countries to put aside their differences to help bring about peace and security.
The United States and Iran have not had diplomatic relations since 1980, and the Swiss Embassy represents U.S. interests in Iran. Washington accuses Iran's Quds Force, an arm of the country's Revolutionary Guard, of aiding Shiite militias in Iraq.
But some signs suggest those tensions are easing: Iraqi and U.S. officials have indicated recently that Iran is using its influence to improve security in Iraq by restraining cross-border weapons flow and militia activity, and U.S. commanders released nine Iranian prisoners in Iraq earlier this month.
"Clearly, we think that there's some value and some worth in keeping this channel open and continuing to be open to having these meetings," McCormack said. "We'll see, over time, what the result is." E-mail to a friend
CNN's Mohammed Tawfeeq ,Thomas Evans and Charley Keyes contributed to this report.