A suicide bomber blew up his vehicle at a checkpoint south of Baghdad and killed four American soldiers, the military said. The US command also announced five soldiers from an elite unit were charged with kicking and punching Iraqi detainees. The suicide attack Monday came as US 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 US 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 terror bombings. The warning's authenticity could not be confirmed.