RAMADI, IRAQ – American troops repelled an attack yesterday by Sunni Arab insurgents who used suicide car bombs, rocket-propelled grenades, and automatic weapons in a coordinated assault against this city’s main government building and two American observation posts.

The fighting in the capital of Anbar province, Ramadi, provided fresh evidence that the insurgency is thriving in Sunni Arab-dominated areas despite last month’s decline in American deaths.

In Baghdad, American and Iraqi forces fought an hours-long gun battle with about 50 insurgents in the Sunni Arab district of Azamiyah, the American military said. Five insurgents were killed and two Iraqi troops were wounded, America said.

There were no reports of American casualties in the 90-minute attack in Ramadi, the second in the past 10 days against the government headquarters for Anbar.

The latest attack began when two suicide car bombers sped toward the government building, known here as Government Center, using a road closed to civilian traffic, Marine Captain Andrew Del Gaudio said.

American Marines fired flares to warn the vehicles to stop. When they refused, the Americans opened fire with .50 caliber machine guns from the building’s sandbagged rooftop. The vehicles turned and sped away but exploded on a main road, sending a huge fireball into the sky and triggering a shock wave that damaged the American post, Captain Del Gaudio said.

As part of the assault, other insurgents fired mortars and rocket-propelled grenades at Marine positions at the roof of the Government Center, which includes the office of the Anbar governor, and at another observation post, Captain Del Gaudio said.

An American Army tank fired a 120 mm shell at a small white mosque where about 15 insurgents were shooting at the Government Center, Captain Del Gaudio said. The round damaged part of the minaret and the firing ceased, he said.

The commander of the 3rd Battalion, 8th Marine Regiment, Lieutenant Colonel Stephen M. Neary, said it was the fourth time in the past 3 1/2 weeks that insurgents had used the mosque to fire on the government building.

The total number of insurgent casualties was unknown. But Lieutenant Carlos Goetz said Marines killed at least three insurgents firing mortar rounds toward the Government Center.

In Baghdad, fighting erupted in Azamiyah before dawn when an Iraqi army patrol came under fire, an American statement said. Four hours later, gunmen attacked an American-Iraqi checkpoint in the area, prompting the command to send American and Iraqi reinforcements. The American statement said clashes continued until early afternoon.

The attack in Ramadi was the biggest since April 8, when insurgents besieged the Government Center until American jets blasted several buildings used by gunmen to fire on the Marines.

American officials had been encouraged by what they described as a relative lull in Anbar, suggesting it was a result of weariness among ordinary Sunni Arabs who were turning against Al Qaeda-led insurgent groups.

Last week, Major General Rick Lynch told reporters in Baghdad that insurgent attacks in Anbar were down to an average of 18 a day – compared to a daily average of 27 last October. At the same time, American deaths for March numbered 31 – the lowest monthly figure since February 2004.

However, American deaths have been rising this month. Of the 47 American service members reported killed in Iraq so far in April, at least 28 have died in Anbar.

Anbar was largely spared the wave of sectarian violence that has swept much of Iraq since the February 22 bombing of a Shiite shrine in Samarra – largely because the province is overwhelmingly Sunni.

Most of the sectarian violence has occurred in Baghdad and other religiously mixed areas. A Shiite cleric was killed last night in southwest Baghdad during a drive-by shooting, police said.

In order to quell sectarian unrest, American officials have been urging the Iraqis to speed up formation of a national unity government of Shiites, Sunnis, and Kurds. The process has stalled because of Sunni and Kurdish objections to the Shiite candidate to head the new government, Prime Minister al-Jaafari.

Prospects for a quick end to the stalemate were in doubt Tuesday as Mr. al-Jaafari’s Dawa party pledged to support him for another term as long as he wants the job. Mr. al-Jaafari has refused to give up the nomination, which he won in a Shiite caucus last February.

Parliament had been set to meet yesterday to try to break the deadlock, but the session was postponed after Shiite politicians gave assurances they could reach a decision on Mr. al-Jaafari themselves without a bruising parliamentary fight.

One option floated called for replacing Mr. al-Jaafari with another candidate from one of the seven parties in the Shiite alliance, Dawa.

But a top Dawa official whose name has been mentioned as a possible replacement, Ali al-Adeeb, said yesterday that the party would not put forward a new candidate unless Mr. al-Jaafari decided to step aside, suggesting further delays.

“Dawa cannot present any candidate unless al-Jaafari decides to step aside,” Mr. al-Adeeb told the Associated Press. “So far his position has not changed.”

Shiite officials, who spoke on condition of anonymity because the issue is sensitive, said some Dawa figures were willing to see Mr. al-Jaafari go in favor of either Mr. al-Adeeb or Jawad al-Maliki. But the party resented outside pressure from Shiites representing other parties as well as from the Americans and British.

The Shiites won 130 of the 275 parliament seats – not enough to govern without the Sunnis and Kurds. Those groups oppose Mr. al-Jaafari, saying he has failed to stop the recent surge in sectarian bloodshed, and neither side has enough votes to force a decision.

Seventeen bodies of people believed victims of sectarian killings were found yesterday, including one in Basra and the rest in Baghdad. They included the body of a brother of a Sunni Arab politician, Saleh al-Mutlaq, Taha al-Mutlaq.