Baghdad, Iraq ? A suspected chemical weapons warehouse 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.

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 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.

Brig. Gen. Mark Kimmitt did not say what sort of chemical munitions were believed to be produced at 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.

The cause of the blast also 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.

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.

Iraqis celebrate as they loot burnt-out U.S. Army Humvee vehicles after an explosion leveled a building in northern Baghdad, setting four Humvees on fire. Two U.S. soldiers were killed and several were wounded in the blast Monday. The cause of the explosion was not immediately known.

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.

Coalition leaders vowed that the latest attacks wouldn’t deter them from returning limited sovereignty to Iraqi control by June 30. They said that most Iraqis supported the United States.

“I have no doubt that television coverage picks up many images of people cheering on attacks on coalition forces,” said Dan Senor, the chief civilian spokesman for the U.S.-led coalition. But “if you look at polling, the silent majority of Iraqis express grateful appreciation.

“They recognize their enemy is our enemy.”