Baghdad, Iraq ? 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-Qaida-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-Qaida 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-Qaida, which has been blamed for some of Iraq’s worst terrorist bombings. The warning’s authenticity could not be confirmed.

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.

Soldiers charged

An Iraqi boy is framed by a damaged door Monday after a mortar shell explosion occurred in the area, in Baghdad, Iraq. Five people were killed in east Baghdad when a mortar shell exploded near a Turkomen club, police said. It was unclear if the club was the target. Four people were injured.

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.

Interrogation defended

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 troop 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.

36 insurgents killed

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.