FALLUJA, Iraq, April 26 — A protracted firefight between marines and insurgents in a residential suburb of this besieged city culminated today with American helicopter gunships and tanks firing at a mosque and toppling the minaret, further dimming hopes for a peaceful end to the three-week siege.
Despite a nominal cease-fire extended by the American authorities on Sunday, the pitched battle lasted several hours, leaving one marine and at least eight insurgents dead by the Americans' count.
The fighting threatened both the truce and a plan to have marines and Iraqi security forces patrol the city together in the coming days. American spokesmen said the patrol plan, advanced by Falluja civic leaders to try to avert an all-out American assault on their city, was still in effect, though some marines on the ground here expressed strong reservations about the effectiveness and trustworthiness of the Iraqi forces.
The American command said the battle erupted in the Jolan section of this Sunni Muslim stronghold 30 miles west of Baghdad when insurgents used the mosque to launch rocket-propelled grenades and small-arms fire at Marine positions. After two hours, pinned down by incoming fire, the Marines called in helicopters and tanks, which directed "suppressing fire" at the mosque, the command said.
"Unfortunately, the opposition forces took it upon themselves to occupy a mosque," Col. John Coleman, chief of staff of the First Marine Expeditionary Force, told reporters. "Instead of serving as a center of religious life, it was employed as a bastion in the attack."
Marine officers look on the resumption of joint patrols with grim foreboding.
With Iraq's prospects of resuming progress toward a peaceful handover of sovereignty on June 30 hanging uneasily in the balance, developments in Falluja were echoed by fresh tensions at Najaf, the holy city 100 miles south of Baghdad that has been the focal point of a separate confrontation.
At nightfall today, Najaf residents said a major battle was under way nearby between American troops and militiamen loyal to Moktada al-Sadr, the rebel Shiite cleric who has taken refuge with supporters in Najaf and an adjacent city, Kufa, defying American threats to kill or capture him.
Sketchy reports of the battle, on a key highway to the city, suggested that Mr. Sadr's fighters had taken heavy casualties from American ground troops backed by helicopter gunships.
American commanders were also closely monitoring reports from inside Najaf said that growing anger of residents there against Mr. Sadr and his militiamen, who have sown a pattern of lawlessness since launching an uprising in the city earlier this month, had taken a startling new turn with a shadowy group of assassins killing at least five Sadr militiamen in attacks on Sunday and Monday.
Those reports, from residents of the city who reached relatives in Baghdad by telephone, said the killings had been carried out by a group calling itself the Thulfiqar Army, after a two-bladed sword that Shiite tradition says was used by Imam Ali, the martyred son-in-law of the Prophet Mohammed, the patron saint of Shiism. Accounts of the killings said the new group had distributed leaflets in Najaf threatening to assassinate members of Mr. Sadr's militia, known as the Mahdi Army, unless they left Najaf immediately.
One Najaf resident said some of Mr. Sadr's militiamen were shedding the black clothing that had been their signature during the weeks that they have occupied Najaf and large parts of other cities in central and southern Iraq with majority Shiite populations.
The same resident said that he knew of two killings of Mahdi Army members on Sunday, near a roundabout in Najaf named for the 1920 tribal revolt against British colonial authority in Iraq, and that three more Sadr militiamen had been killed later on Sunday or Monday.
If reports of violence against Mr. Sadr's followers in Najaf suggested that the American occupation authority might finally be seeing the beginnings of Iraqis taking action of their own to curb the firebrand cleric — as the American administrator, L. Paul Bremer III, recently urged in a television address — events in Baghdad today underscored how potent a force Mr. Sadr remains, at least among many volatile young Shiites who have found a release from their impoverishment in the cleric's anti-American rhetoric.
The latest outburst of fury against the American occupation came when American troops raiding a chemical storage warehouse in one of the capital's inner-city neighborhoods were caught in a huge explosion that sent a pillar of white smoke roiling hundreds of feet into the air and tons of masonry cascading down onto a busy street. The American command said two soldiers had been killed and five others had been injured; at least eight Iraqi civilians were hurt, and four American Humvee vehicles were set afire.
American military spokesmen withheld details of what caused the blast. One eyewitness report suggested that the cause was a spark that coincided with the troops' breaking into the warehouse; another possibility was that the Americans, belonging to the Iraq Survey Group, a unit set up to search for stockpiles of forbidden weapons, could have stumbled into a trap. An informant had told the American command that the chemical store's owner and his associates were supplying chemical agents to "terrorists, criminals and insurgents," as a command statement put it.
In any case, the explosion set the scene for yet another of the frenzied demonstrations of anti-American feeling that have occurred when American troops are attacked, with young Iraqi men dancing on top of burning Humvees and shouting "Moktada! Moktada!" for the rebel cleric.
Others rushed up to television crews with American helmets, and placed one on the head of a donkey; still others ran down the street displaying charred remnants of chemical-weapons clothing pulled from the Humvees, some with shoulder patches bearing the survey group's motto, "Find, exploit, eliminate."
In Falluja, the marines on the ground showed little enthusiasm for the tentative extension of the cease-fire, which was cobbled together at the last minute by Mr. Bremer as top political and military leaders contemplated the potentially disastrous public relations impact of a bloody attack on the city.
"This isn't a cease-fire," a Marine officer snorted. "It's a chance for them to regroup."
That view gained credence with today's fighting, which began late this morning in the Jolan section, in the northwest quarter of the city, near a sharp bend in the Euphrates River. Old and poor, the neighborhood is known as a stronghold of the insurgents.
As a Marine platoon tried to move forward to secure a better position in the area, it came under heavy rocket-propelled grenade fire from insurgents based in a mosque, reporters traveling with the unit said.
Tanks were called in and, eventually, air support. A Cobra attack helicopter fired a missile that toppled the mosque's minaret, witnesses said. Two dark pillars of smoke rose in the air.
Not only is the effectiveness of the Iraqi security forces in doubt, in the Marines' eyes, but so is their loyalty. During the previous weeks of fighting, they dropped out of sight, some lying low, others going over to the insurgency.
It is further unclear how many Iraqi security forces will show up for duty, as is the degree of their enthusiasm. And there are worries among the Marines that they may turn on the Americans or lead them into an ambush. The Marine contingency plans for the patrols call for a heavy response if they are fired upon.
In a separate incident during the day, marines exchanged fire with insurgents in the Shuhada district in the south-center of the city, another opposition stronghold. A Marine officer on the scene said the fighting started when a patrol came upon armed men setting up roadblocks.
John Kifner reported from Falluja and John F. Burns reported from Baghdad for this article.