A suicide bomber blew up his vehicle at a checkpoint south of Baghdad and killed four American soldiers Monday, the military said. The U.S. command also announced five soldiers from an elite unit were charged with kicking and punching Iraqi detainees.

The suicide attack came as U.S. and Iraqi troops battled Al Qaeda-led militants for a third day in Husaybah, a town on the Syrian border that the military describes as a major entry point for foreign fighters. One Marine has died there, the U.S. command said Monday.

Al Qaeda in Iraq warned the Iraqi government to halt the offensive in Husaybah within 24 hours or see "the earth ... shake beneath their feet."

"Let them know that the price will be very heavy," said an Internet statement purportedly issued by Al Qaeda, which has been blamed for some of Iraq's worst terror bombings. The warning's authenticity could not be confirmed.

Meanwhile, the Pentagon announced a troop rotation for Iraq that will number at least 92,000 soldiers through 2008, although officials said it likely will be considerably larger.

The four soldiers who died in the suicide attack were assigned to the Army's Task Force Baghdad, the U.S. command said, offering no further details. Earlier Monday, the military said a U.S. soldier died Sunday in a roadside bombing near Tikrit.

The deaths brought to at least 2,051 the number of U.S. military personnel who have died since the Iraq war started in 2003, according to an Associated Press count. At least 24 have died this month — most in roadside bombings.

The U.S. military said five soldiers from the Army's 75th Ranger Regiment were charged Saturday with assault, maltreatment and dereliction of duty during a Sept. 7 incident "in which three detainees were allegedly punched and kicked while awaiting movement to a detention facility." All five were reassigned to administrative duties, the statement said.

The Army said the alleged incident occurred in Baghdad and that the detainees, all men, suffered bruises "caused by striking with a closed and open hand, kicking, and hitting with an object described as a broomstick."

Allegations of prisoner abuse at the Abu Ghraib prison in Baghdad gained international notoriety in 2004. Nine Army reservists were convicted in that scandal.

The announcement of fresh abuse charges came as President Bush defended U.S. interrogation practices in the war on terrorists and lobbied against a congressional drive to outlaw torture.

The newly announced troop rotation is smaller than the one currently in Iraq, but a Pentagon spokesman, Lt. Col. Barry Venable, said no decisions have been made to reduce troops levels next year.

The U.S. has maintained a roughly 138,000-strong troop level in Iraq throughout the year, expanding it to 160,000 this fall because of the Oct. 15 Iraqi constitutional referendum and Dec. 15 election.

Monday's announcement did not include any Marine Corps units, although they apparently will be added later.

Defense Secretary Donald Rumsfeld said conditions in Iraq in coming months would determine any changes in U.S. force levels.

In a statement Monday on the Husaybah fighting, the Marines said American and Iraqi troops were trying to flush out insurgents in mosques, schools and other public buildings but did not say how much of the town had been secured.

The statement said at least 36 insurgents had been killed since the assault began Saturday in the town 200 miles northwest of Baghdad. A Marine commander gave the same figure Sunday night.

"Our strategy is basically to kill the insurgents when we come across them," Marine Capt. Conlon Carabine told CNN on Monday.

Carabine said U.S. and Iraqi troops would establish a long-term presence in the town after rooting out the insurgents.

A Marine statement said three insurgents disguised as women tried to enter a camp for displaced civilians in Husaybah on Monday but were killed by Iraqi guards who spotted their weapons. The statement also said Marines found the booby-trapped body of an insurgent in a school.

In Baghdad, a Sunni Arab politician, Adnan al-Dulaimi, urged U.S. and Iraqi forces to halt military offensives in Sunni towns like Husaybah, saying that would help encourage disaffected Sunnis to vote in elections next month.

Iraq's insurgency is primarily based within the Sunni Arab minority, which was the dominant group during Saddam Hussein's reign.

Al-Dulaimi said U.S. and Iraqi commanders should "halt their attacks against cities and take into consideration that innocent people should not be punished because of the actions of others."

He nonetheless urged Sunnis not to boycott the Dec. 15 legislative elections. The decision by many Sunnis to stay away from the polls during last January's vote enabled rival Shiites and Kurds to win an overwhelming majority in the current legislature.

"We will participate in the next elections in order to save Iraq, and I call upon all political entities not to boycott the elections," al-Dulaimi said.

Elsewhere, five people were killed and four were wounded Monday in east Baghdad when a mortar shell exploded near a club for members of the Turkomen ethnic minority, police said. It was unclear if the club was the target.

A roadside bomb killed six policemen and three civilians in the capital's southern Dora neighborhood, an insurgent stronghold, said Mohanad Jawad, an official at Yarmouk Hospital. Insurgents have targeted policemen and soldiers because they consider them agents for foreign troops.

In the northern city of Mosul, three gunmen burst into an Internet cafe and killed a journalist from the Turkomen minority, Ahmed Hussein al-Maliki, police said. The motive was unclear but journalists have been targeted in Mosul in the past.

A suicide car bomber exploded his vehicle near an Iraqi army unit responsible for guarding oil pipelines south of Kirkuk, killing one Iraqi soldier, police said.

Three attacks in southern Iraq apparently targeted Japanese troops, injuring a policeman and a taxi driver, the Kyodo News agency reported. Japan has some 600 non-combat troops in Samawah working on humanitarian projects.