BAGHDAD, Iraq – American soldiers battled insurgents northeast of Baghdad yesterday in clashes that killed more than 50 people. Some guerrillas were said to be “fighting to the death” inside Fallujah, where American forces struggled to clear pockets of resistance.

At least five suicide car bombers targeted American troops elsewhere in volatile Sunni Muslim areas north and west of the capital, wounding at least nine Americans. Three of those bombings occurred nearly simultaneously in locations between Fallujah and the insurgent stronghold of Ramadi, the American command said.

The zone between Fallujah and Ramadi was one of at least three areas yesterday in which insurgents pulled off almost-simultaneous attacks against American or Iraqi forces, suggesting a level of military sophistication and planning not seen in the early months of the insurgency last year.

Pressing their own offensive in central and northern Iraq, insurgents attacked police stations, Iraqi security forces, American military convoys, and oil installations across a wide area of the Sunni heartland.

In a speech found yesterday on the Internet, a speaker said to be Abu Musab al-Zarqawi, the country’s most feared terror leader, called on his followers to “shower” the Americans “with rockets and mortars” because American forces were spread too thin as they seek to “finish off Islam in Fallujah.”

The worst reported fighting yesterday took place about 35 miles northeast of Baghdad after assaults, at al most the same time, on police stations in Baqouba and its twin city, Buhriz.

Gunmen abducted police Colonel Qassim Mohammed, took him to the Buhriz police station, and threatened to kill him if police didn’t surrender the station. When police refused, the gunmen tied the colonel’s hands behind his back and shot him dead.

American and Iraqi troops rushed to the scene, setting off a gun battle that killed 26 insurgents and five other Iraqi police officers, Iraqi officials said.

At the same time, insurgents attacked a police station in Baqouba and seized another building. American aircraft dropped two 500-pound bombs before the end of the fighting, in which four American soldiers were wounded, the American command said.

During the fighting, American troops came under fire from a mosque, the American military said. Iraqi security stormed the mosque and found rocket-propelled grenades, mortar rounds, and other weapons and ammunition, the statement said.

In one of the car bombings along the Fallujah-Ramadi corridor, the attacker rammed into a Marine armored vehicle, wounding the four troops inside. The two other bombings caused no injuries – including one in which the driver rammed his car into a tank but his explosives failed to detonate.

Witnesses reported a fourth car bombing late yesterday in Ramadi against an American convoy, but there was no report of casualties.

In Mosul, where an uprising broke out last week in support of the Fallujah defenders, a suicide driver tried to ram his bomb-laden vehicle into an American convoy, the military said. He missed but set off the explosives, wounding five soldiers, four of them slightly.

Four American soldiers were wounded when their patrol ran over a land mine yesterday near Beiji in northern Iraq, the military said. Saboteurs blew up an oil pipeline yesterday, shutting down Iraqi oil exports from the north, and set fire to a storage and pumping station in northern Iraq, officials said.

In Baghdad after nightfall yesterday, heavy explosions rocked the Green Zone – the barricaded neighborhood that houses the Iraqi government and American embassy. Loudspeakers warned, “Take cover, take cover.”

Gunmen carried out near-simultaneous attacks on a police station and an Iraqi National Guard headquarters in Suwayrah, 25 miles south of Baghdad, killing seven Iraqi police and soldiers.

During a news conference in Baghdad, the interior minister, Falah Hassan al-Naqib, himself a Sunni, condemned the growing attacks on Iraqi police and security forces, calling them part of a campaign “to divide this country and thrust it into a civil war.”

Separately, an American Marine shot and killed a wounded and apparently unarmed Iraqi prisoner in a mosque in the former insurgent stronghold of Fallujah, according to dramatic pool TV pictures broadcast yesterday. A Marine spokesman in Washington said the shooting was under investigation.

The shooting Saturday was videotaped by pool correspondent Kevin Sites of NBC TV, who said three other previously wounded prisoners in the mosque apparently had also been shot, again by the Marines inside the mosque.

The incident played out as the Marines 3rd Battalion, 1st Regiment, returned to the unidentified Fallujah mosque Saturday. Mr. Sites was embedded with the unit.