Iran called off further Iraq security talks with Washington until U.S. forces stop their crackdown on Shiite militias, but the military brought more air power into the fight Monday and escalated its accusations of Iranian backing for extremists.
The flare-up has put Iraq's government in a bind as it seeks to stamp out armed Shiite gangs but worries about angering its Shiite neighbor to the east, which has close ties to Iraq's political leadership.
Washington has long accused Iran of arming and training some Shiite militia factions. The accusations sharpened Monday as the military said detainees described being trained at bases outside Tehran by militants from Hezbollah, an Iranian-aided faction based in Lebanon.
Iraq's Shiite-led government said battles against militias would continue even if Iran pulled out of the security talks. Three rounds have been held at the ambassador level since May, marking rare direct diplomatic contact between Iran and the United States.
There are also worries that Sunni extremists are regrouping. Attacks blamed on Al Qaeda in Iraq have claimed dozens of lives in recent days, including an attack Monday that killed at least 10 Iraqi soldiers and wounded 13 at a checkpoint in Diyala province northeast of Baghdad, the U.S. military said.
In Tehran, Iran's Foreign Ministry spokesman Mohammed Ali Hosseini said talks could not be held under current conditions.
"What we are witnessing is open and extensive bombing of the Iraqi nation, while the main goal of talks with the American side would have been security and peace in Iraq," Hosseini said. "It is a matter of doubt that the U.S. is pursuing a solution for the crisis, which was caused by them."
In Baghdad's Sadr City, a Shiite area populated by 2.5 million people, U.S. and Iraqi forces have been under sustained attacks by militias including members of the powerful Mahdi Army led by anti-American Shiite cleric Muqtada Sadr.
On Monday, the U.S. Air Force unleashed one of its most potent weapons, the AC-130 gunship, against Shiite militants in Baghdad. The U.S. military said it killed at least nine militants in clashes since Sunday.
Many recent attacks against U.S. forces have been blamed on armor-piercing bombs that the Pentagon says are partially manufactured in Iran.