BAGHDAD - 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 latest flare-up has put Iraq's government in a bind as it seeks to stamp out armed Shiite gangs but worries about angering Shiite heavyweight Iran, which has close ties to the core of Iraq's political leadership.

Washington has long accused Iran of arming and training some Shiite militia factions. The accusations were sharpened Monday as the military said detainees had 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 will continue even if Iran pulls out of the security talks. Three rounds have been held at the ambassadorial level since May and marked rare direct diplomatic contact between the two nations, which have had no formal relations since shortly after Iran's 1979 Islamic Revolution.

In Tehran, Iran's Foreign Ministry spokesman Mohammad 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 slum where 2.5 million people live, U.S. and Iraqi force have been under sustained attacks by militias, including members of the powerful Mahdi Army led by anti-American cleric Muqtada al-Sadr.

Hundreds of people have been killed in Baghdad and the southern city of Basrah since late March, when Iraq's prime minister, Nouri al-Maliki, launched an offensive against Shiite militias and so-called "special groups" with suspected ties to Iran.