BAGHDAD (AP) – American ground forces and helicopters fought with gunmen around a Shiite mosque in western Baghdad before Friday prayers, killing two suspected insurgents, the American military said.

The military first denied reports by witnesses and Iraqi TV that American helicopters had fired near the blue-domed mosque in Baiyaa, a religiously mixed neighborhood in western Baghdad. Several hours later, however, the military said a review of the firefight indicated that its helicopters had fired about 100 rounds of 30mm ammunition.

Soldiers searching nearby buildings found chemicals believed to be bomb-making materials and detained an Iraqi civilian, the military said. Iraqi soldiers searched the Ali al-Baiyaa mosque, but found no weapons or suspects.

The coalition suffered no casualties, and damage to the mosque was limited to several small bullet holes, an AP photographer on the scene said.

In the holy city of Kufa, 100 miles south of Baghdad, Abdul Hadi al Mohamadawi, a sheik loyal to radical Shiite cleric Muqtada al-Sadr, used his sermon at the Kufa mosque to condemn American forces.

“American forces are conducting an offensive on a mosque in al- Baiyaa, and martyr worshippers are falling,” he said. “Let the government see what the occupiers are doing to our people.”

On Monday, Mr. al-Sadr’s six ministers quit the Iraqi Cabinet to protest Prime Minister Nouri al-Maliki’s refusal to back calls for a timetable for American withdrawal.

Also Friday, the American military announced the death of a Marine in a rocket attack the night before on a base south of the capital. Two others were wounded in the attack on an American base in Mahmoudiya, about 20 miles south of Baghdad, a statement said.

Mr. al-Maliki said Thursday that an “open battle was being waged for control of Iraq,” a day after more than 230 people died in the worst spasm of mass killings since President Bush announced his plan in January to increase American troop levels in Iraq by 30,000.

Three of the five brigades ordered into Iraq by Mr. Bush to stem Baghdad’s violence have arrived, bringing the American forces in the country to 146,000. Officials want the rest in place by June, for a total of 160,000, and American commanders urged patience, saying the nine-week operation was still just beginning. But already it showed holes.

About a week ago, a suicide bomber penetrated several layers of security to hit inside parliament, in the heart of the American-guarded Green Zone. An Iraqi lawmaker was killed. The same day, a truck bomber collapsed a more than 50-year-old bridge, killing 11 people and sending cars careening into the Tigris River below.

In an earlier breach, a bomber targeted Iraq’s Iraq’s Sunni Arab deputy prime minister, Salam al-Zubaie, at a small mosque attached to his home. Mr. al-Zubaie, who was injured in the attack, said in remarks aired Friday that an “Arab terrorist” was behind the attack, not one of his guards as earlier reported.

At the Pentagon Thursday, a top general predicted the pattern was likely to continue.

“We saw an initial drop in their (militants’) activity” after the start of the Baghdad security operation, said Major General Michael Barbero, an operations official for the Joint Chiefs of Staff. “And now lately, we’ve seen an increase.”

He said the violence was likely to continue “until we can defeat these forces.”

Mr. al-Maliki said militants had “proven their spite by targeting humanity.”

“It is an open battle and it will not be the last in the war we are fighting for the sake of the nation, dignity, honor and the people,” he said at a ceremony marking the 50th anniversary of the founding his Islamic Dawa Party.

On Thursday afternoon in Latifiyah, about 20 miles south of the capital, gunmen attacked a convoy belonging to the son of Abdul Aziz al-Hakim, head of the country’s most powerful Shiite political party, the Supreme Council for the Islamic Revolution in Iraq. Ammar al-Hakim escaped unharmed, but two of his bodyguards and four policemen were wounded.

Meanwhile, American forces killed eight suspected insurgents and captured 41 in several raids across Iraq on Friday, the military said.