The U.S. and Iranian ambassadors to Iraq met Monday for their third round of talks on security in Iraq in just over two months, a U.S. official said, despite renewed military claims that Tehran is fueling the violence.

U.S. Ambassador Ryan Crocker met with his counterpart Hassan Kazemi Qomi for about two hours after U.S., Iraqi and Iranian experts held their first talks as part of a security subcommittee, according to the U.S. Embassy.

The high-level discussions were "frank and serious," embassy spokesman Philip Reeker said.

He said they were held at the office of Iraq's National Security Adviser Mouwaffak al-Rubaie but gave no further details.

Washington has accused Tehran of fueling the violence by arming and training Shiite extremists, but Crocker and Qomi agreed during their July 24 talks to set up a security subcommittee to carry forward talks on restoring stability in Iraq.

The subcommittee also met for the first time on Monday in Baghdad, with the three sides sitting around three conference tables at an Iraqi government office in the heavily fortified Green Zone.

The diplomatic activity came a day after the No. 2 U.S. military commander in Iraq, Lt. Gen. Raymond Odierno, blamed Iran for sharply increasing its support in providing weapons and training to rogue Shiite militiamen who he said had launched 73 percent of the attacks that killed or wounded American forces last month in Baghdad.

That was nearly double the figure six months earlier, Odierno said, adding he believes Iran is trying to influence public opinion ahead of a pivotal September report due to U.S. Congress on political and military progress in Iraq.

Tehran has consistently denied the U.S. allegations.

On Monday, the Iranian delegation criticized what it called America's "suspicious" security approach toward Iraq and called for "a change in the broad policies and approach of the U.S." in Iraq during the expert-level talks, according to the official Islamic Republic News Agency.

The report, which did not mention the ambassadorial meeting, said the Iranians cited specific suspect cases but it did not elaborate.

IRNA also reported that the Iranian delegation enumerated the U.S. "support for veteran (militant) elements, giving terrorists a free hand in specific locations in Iraq" as well as the "weak points of the U.S. security-political plan in Iraq."

The agency said the Iranian delegation insisted on Tehran's support for Nouri al-Maliki's government to establish security and bring stability to Iraq, an apparent reference to the political crisis surrounding the Shiite leader.

Iran holds considerable sway in Iraq, where the majority of the population is also Shiite Muslim and where Shiite political parties have close ties to Tehran. Al-Maliki was slated to visit the Islamic republic Wednesday, a day after a trip to Turkey. His government has said it wants good relations with Iran while insisting there should be no interference in its internal affairs.

IRNA said the U.S. delegation called the security situation in Iraq "difficult" and called for Iran's assistance in finding a solution to get out of the current situation.

The detention of four Iranian-Americans in Iran has deepened tensions between Washington and Tehran, whose relations were already strained over Iran's nuclear program and its support for radical militant groups like Lebanon's Hezbollah and the Palestinian Hamas and by U.S. military maneuvers in the Persian Gulf. Washington has called for their release and says the charges are false.

The embassy said Monday's discussions focused on the violence plaguing Iraq. The American delegation to the expert talks was led by the U.S. Embassy's counselor for political and military affairs Marcie B. Ries.

"We agreed to continue our discussions at a date to be established through diplomatic channels," Reeker said. "We appreciate the role played by the government of Iraq in chairing the meeting."

In Washington, State Department spokesman Sean McCormack described the session as professional and useful, adding that another will be held at some point.

The meetings were welcomed by the fragile Iraqi government, which has called on both sides not to let their tensions disrupt efforts to bring stability to Iraq.

President Jalal Talabani expressed hope the experts meeting would "succeed in achieving security and stability in Iraq," his office said. "The president hopes that Iran will play a positive role in finding a way to achieve the ambitions of the Iraqi people."

The first round of Iran-U.S. talks, on May 28 in Baghdad, broke a 27-year diplomatic freeze following the 1979 Islamic Revolution and U.S. Embassy takeover in Tehran. Former U.S. Ambassador Zalmay Khalilzad saw Iranians on the sidelines of a Mideast meeting earlier this year and both he and Crocker met privately with Iranians over Afghanistan after the Sept. 11, 2001, attacks when the U.S. was headed into Afghanistan to depose the Taliban.