About 100 masked gunmen stormed a prison near the Iranian border Tuesday, cutting phone wires, freeing all the inmates and leaving behind a scene of devastation and carnage — 20 dead policemen, burned-out cars and a smoldering jailhouse.

At least 10 attackers were killed in the dawn assault on the Muqdadiyah lockup on the eastern fringe of the Sunni Triangle, police said. The raid showed the mostly Sunni militants can still assemble a large force, capable of operating in the region virtually at will — even though U.S. and Iraqi military officials said last year that the area was no longer an insurgent stronghold.

The insurgency's strength, spiraling sectarian violence and the stalemate over forming a government in Iraq have led politicians and foreign policy experts to say Iraq is on the brink or perhaps in the midst of civil war.

In all, 33 prisoners were freed, including 18 insurgents who were detained Sunday during raids by security forces in the nearby villages of Sansal and Arab, police said. It was the capture of those insurgents that apparently prompted Tuesday's attack. The 15 other inmates were a mix of suspected insurgents and common criminals.

In an Internet posting Tuesday night, the military wing of the Mujaheddin Shura Council, a militant Sunni Muslim insurgent group, purportedly claimed it carried out the operation. The posting said the group killed "40 policemen, liberated 33 prisoners and captured weapons."

The claim was posted on the Iraqi News Web site. Neither the higher casualty toll among policemen nor the captured weapons could not be independently verified.

The cutting of the telephone lines made it impossible for jailers or security men, who apparently did not have cell phones, to call other police for backup. Residents of the town informed authorities of the situation after hearing the firing.

With the wires cut, the insurgents had 90 minutes to battle their way into the law enforcement compound before police reinforcements showed up from the nearby villages of Wajihiyah and Abu Saida, police said. Muqdadiyah is about 25 miles from the Iranian frontier and 60 miles northeast of Baghdad.

By the time the insurgents fled, taking away the bodies of many of their dead compatriots, nearly two dozen cars were shot up and set on fire and the jail was a charred mass of twisted bunk bed frames and smoldering mattresses.

Afterward, U.S. helicopters hovered in the air above the jail. Police said residents fired into the air, but it was not clear if the American aircraft were the target. None was hit.

It was not the first time militants have targeted a jail.

On April 20, 2004, insurgents fired 12 mortars into the infamous Abu Ghraib prison on the outskirts of Baghdad, killing 22 inmates and wounding 92. A U.S. general speculated the attack may have been an attempt to spark a prison break or an uprising.

In other violence Tuesday, a roadside bomb killed one policeman and wounded three in Baqouba, 35 miles northeast of Baghdad, authorities said.

A U.S. soldier with the 4th Infantry Division was killed by small-arms fire Tuesday while patrolling western Baghdad, the U.S. military reported. At least 2,315 members of the U.S. military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

Also in the capital, gunmen killed an employee of the mayor's office while he was driving in the Dora neighborhood of south Baghdad.

Police reported discovering eight more blindfolded corpses in west Baghdad, some of them under a highway and showing signs of torture, officials said. In Suwera, 50 miles south of Baghdad, four more corpses were found on the bank of the Tigris River.

The execution-style killings have become an almost daily occurrence in a wave of sectarian violence that has left more than 1,000 Iraqis dead since the bombing last month of a Shiite shrine.

With an increasing number of Americans calling for a pullout of U.S. forces regardless of the consequences for Iraq, a powerful group of U.S. senators met with interim Prime Minister Ibrahim al-Jaafari on Tuesday to discuss prospects for formation of a national unity government.

The Bush administration views that step as all-important in establishing peace and opening the way for the start of a U.S. troop withdrawal as early as this summer.

Al-Jaafari said he believed Iraq's most difficult political hurdles had been crossed and predicted a new government would be ready in the coming weeks.

"I hope that the formation of the new government does not last beyond April," he said after the meeting.

Sen. Carl Levin of Michigan, ranking Democrat on the Senate Armed Services Committee, said: "April is fine, but it is necessary that this commitment be kept in order for there to be continued support for the presence of American troops in Iraq."

However, President Bush said Tuesday that the decision about when to withdraw all U.S. troops from Iraq will fall to future presidents and Iraqi leaders, suggesting that U.S. involvement will continue at least through 2008.