A top U.S. military commander in Iraq says militant mortar and rocket attacks on Baghdad's fortified Green Zone have been more accurate over the past three months because of training in Iran.
Lieutenant General Raymond Odierno said Thursday there has been "significant improvement" in the capability of militias and their firings have been more accurate.
He said the military thinks "this is directly related to training conducted inside Iran."
General Odierno made the remark two days after U.S. and Iranian ambassadors to Iraq held a second round of talks in Baghdad on Iraq's security.
U.S. Ambassador Ryan Crocker said there were some "heated exchanges" when he told his Iranian counterpart, Hassan Kazemi Qomi, that Iranian support for Shi'ite militias in Iraq has risen since they held the first round of talks on the issue in May.
Iran has denied supplying weapons and training to Shi'ite militias in Iraq.
Iran, Iraq, and the U.S. agreed to create a security committee on Iraq. But Crocker said no progress can be made unless Iran changes its behavior in Iraq.
On Wednesday, The United States also rejected an Iranian suggestion to hold higher-level talks on the security situation in Iraq.
U.S. State Department spokesman Sean McCormack said he does not see talks between the U.S. and Iran at the level of deputy foreign minister at this time. McCormack said the two sides have already established a diplomatic channel between their ambassadors in Iraq.
The United States broke diplomatic relations in April, 1980 after Iranian activists seized the U.S. Embassy in Tehran and took its staff hostage.
Relations between Iran and Iraq have improved since the ouster of Saddam Hussein as Iraqi leader. Both countries have Shi'ite majorities. Saddam's Sunni-led government fought Iran in the 1980-88 Iran-Iraq war.
Some information for this report was provided by AP and Reuters.