Updated

Just one day after U.S. officials announced that a fragile cease-fire in Fallujah (search) was being extended, Marines were engaged Monday in an intense firefight with insurgents in a northern district of the besieged Iraqi city.

A Baghdad workshop believed to be producing chemical munitions (search) exploded in flames Monday moments after U.S. troops broke in to search it, killing two soldiers and wounding five. Jubilant Iraqis swarmed over the Americans' charred Humvees, waving looted machine guns, a bandolier and a helmet.

Brig. Gen. Mark Kimmitt (search) did not say what sort of chemical agents were suspected of being supplied to insurgents from the Baghdad warehouse. After the blast, there was no sign of precautions against chemicals.

"Chemical munitions could mean any number of things," including smoke grenades, he said.

In Fallujah, U.S. troops came under a heavy insurgent attack a day after U.S. officials decided to extend a cease-fire rather than launch a full-scale offensive on the city. One Marine and eight insurgents were killed.

Marines battled Sunni (search) guerrillas around a mosque in Fallujah's Jolan district, a poor neighborhood where insurgents are concentrated. Helicopter gunships joined the battle, which sent heavy black smoke over the city. Tank fire demolished a minaret from which officials said gunmen were firing.

The U.S. troops met "a real nasty bunch," said Lt. Col. Brennan Byrne, commander of the 1st Battalion, 5th Marine Regiment. But he said the violence would not deter plans to begin joint U.S.-Iraq patrols in the city.

The patrols are a key part of the U.S. effort to establish a semblance of control over Fallujah without a wider Marine assault, which would revive the bloody warfare seen earlier this month. The United States decided to try the patrols after President Bush consulted with his commanders over the weekend, and the cease-fire was extended in part to allow for patrols to be organized.

The cause of the Baghdad warehouse blast was unclear. Kimmitt said a large number of explosives were in the building, located in the northern neighborhood of Waziriyah.

Asked about reports that the search team included members of the Iraq Survey Group -- the U.S. team looking for weapons of mass destruction -- Kimmitt said only: "The inspection was by a number of coalition forces."

He said the owner of the site was "suspected of producing and supplying chemical agents" to Iraqi insurgents, but did not elaborate.

The blast leveled the front half of the one-story building and set ablaze four Humvees parked outside. A U.S. soldier was taken away on a stretcher, her chest and face severely burned. Several Iraqis were pulled from the wreckage, including a woman who wept as she was carried over a man's shoulder to safety.

Afterward, dozens of cheering teenagers started to smash the abandoned Humvees. One child climbed on a hood of one of the vehicles and beat it with a stick. A man held up a photo of radical Shiite cleric Muqtada al-Sadr. Iraqis stripped the vehicles of equipment, one carrying a heavy machine gun, another waving a U.S. helmet. One man sported military headphones.

"This is for the madman Bush, for the madman Bremer!" said one youth as he waved a rifle, referring to President Bush and the top American administrator in Iraq, L. Paul Bremer.

In the south, outside the holy city of Najaf, Shiite militiamen in cars fired rocket-propelled grenades at a U.S. position, witnesses said. Apache helicopters and U.S. troops opened fire and set the cars ablaze.

The clash came as around 200 U.S. troops and Military Police made their first deployment inside Najaf, moving into a base that Spanish troops are vacating about five miles from holy shrines at the heart of the city.

U.S. commanders have said they will not move against the shrines in order to capture al-Sadr. The Americans say they're aware that doing so could turn the cleric's limited revolt into a wider anti-U.S. uprising by Iraq's Shiite majority.

In Baghdad, however, Bremer heightened warnings about the reported stockpiling of weapons in "mosques, shrines and schools" in Najaf -- and his spokesman noted that such actions make the sites fair targets for military action.

"The coalition certainly will not tolerate this situation," Bremer said in a statement addressed to residents of Najaf. "The restoration of these holy places to calm places of worship must begin immediately."

Bremer's spokesman, Dan Senor, would not elaborate on steps the coalition was ready to take to do so. He noted that in the case of military action, "those places of worship are not protected under the Geneva Convention" if they are used to store weapons.

Shiite militias remain a threat in other cities.

Militiamen ambushed Spanish troops in the city of Diwaniyah, south of Najaf, and in the ensuing battle, six Iraqi gunmen were killed. Insurgents in Karbala fired at Bulgarian President Georgi Parvanov's motorcade Sunday as he made a brief visit to his country's troops. No one in the motorcade was hurt.

The deaths of the two soldiers in Baghdad and the Marine in Fallujah brought to 114 the number of U.S. troops killed in combat so far this month -- nearly as many as the 115 Americans killed during the invasion that toppled Saddam Hussein a year ago.

The fighting in Fallujah was the latest violence to shake a two-week-old cease-fire.

Still, U.S. officials said they wanted to press forward with a political track, a day after abruptly toning down threats to launch a full-out assault on the city.

"We will take the time necessary to see if there is not a political solution," Secretary of State Colin Power said Monday. "But as you saw today, when our soldiers and our Marines are attacked, they will respond and they will respond with force to protect themselves."

U.S. troops and Iraqi security forces are to start patrolling most parts of the city, except the Jolan area, probably on Thursday. There was little guarantee that guerrillas, who Marines say have not abided by other parts of past negotiated agreements, won't attack the patrols.

In Najaf, the Spanish base is pockmarked with shells and shrapnel from earlier attacks. The golden domes of the Shiite shrines at Najaf's center -- a no-go zone for the Americans -- were visible from inside the compound. Spanish troops are due to leave within days, and the Americans moved in to ensure al-Sadr militiamen did not overrun the site.

The move also gives U.S. forces a foothold in Najaf from which to pressure al-Sadr. He is holed up in the center of the city near the shrines, where his militiamen largely control the streets.

The base, which houses Salvadoran and Spanish troops, is in the modern part of Najaf, an urban extension that melds with the neighboring city of Kufa.

The U.S. military will take over security duties throughout Najaf province and the neighboring province of Qadisiyah after the withdrawal of Spanish, Dominican and Honduran forces this month, said a Polish spokesman, whose country's forces lead multinational peacekeepers in the area.

The extension of U.S. forces would be a major reversal of American efforts to hand security duties in the south to its allies. But the coalition has been frayed by the Spanish-led pullout and the eruption of fighting in the previously more peaceful south.

The Associated Press contributed to this report.