As U.S. strikes on Shiite armed fighters in Baghdad have widened, Iran has suspended talks with the United States on Iraqi security, citing the continued offensive as the reason, the Iranian Foreign Ministry said Monday.

American forces were responding to fire from Shiite militias in the Amel neighborhood in western Baghdad, and in eastern Baghdad, they hammered both the nearby district of New Baghdad during the day and the Shiite ghetto of Sadr City on Monday night.

"The focus of discussions with the U.S. is Iraq's security and stability," said Mohammad Ali Hosseini, the spokesman for the Iranian Foreign Ministry in Tehran, according to IRNA, the official Iranian news agency.

"We are witnessing indiscriminate bombardment of Iraqi residential areas by the U.S. occupying forces," Hosseini told reporters at his weekly news conference.

The United States says Iran is supplying weapons and training to Shiite militias in Iraq, but Tehran has denied interfering. It remains uncertain whether some of the weapons found in Iraq that appear to be Iranian came directly from Iran or through third parties.

The Iraqis are forming a committee with experts from the ministries of interior and defense to look into the allegations against Iran.

The State Department did not comment directly on the talks, but a spokesman, Tom Casey, said: "The fact remains, though, that the Iranian government continues, despite their public statements of support for the Iraqi government, to play this negative role, to provide this kind of assistance to militant groups and to militia groups.

"It's something we want to see stopped, and it's something the Iraqis want to see stopped," Casey said.

The gesture by Iran is hard to read. It comes on the heels of a disclosure by the U.S. military that among the evidence it has collected of intervention by Iran is documentation of training camps near Tehran run by Lebanese Hezbollah militants. That information was given to an Iraqi delegation to present to Iranian officials last week. But Iranian politics is a game of shadows, with so many crosscutting interests that it is hard to say what Iran's goal may be in suspending the talks.

Two things are clear: The talks have not borne much fruit, so suspending them is almost cost-free, at least in the short term. The downside is that the talks have been a way for the two countries, which do not have diplomatic relations, to have face-to-face conversations. Several Iraqi politicians said they believe that the Iranian suspension was as much in retaliation for U.S. criticism of Iran's nuclear program as it was for Iraq policy.

"Some Iranian officials believe that Iraq is a better location to pressure the Americans over Iran's diplomatic crisis with them," Ali al-Dabbagh, Iraq's government spokesman, told Al Hurra, a satellite channel, Monday evening.

Secondly, Iran loses nothing in Iraq by denouncing strikes on Shiite civilians, especially since it has also said it approves of the Iraqi government's effort to halt the activities of illegal militias. While those two positions might sound contradictory, in fact, they are plausible here. The Iraqi government also says it wants to help civilians and is only targeting the militias. The reality is that when forces go after insurgents in urban areas, it is impossible to avoid hitting some innocents as well.