The second explosion killed two Iraqi civilians south of Baghdad.

Also Tuesday, two bombs exploded minutes apart near a square in central Baghdad, killing at least seven people and wounding about 20, police and hospital officials said.

The first bomb was in a plastic bag placed near a CD vendor's stand close to Tahrir Square by a man who fled seconds before the explosion at 9:55 a.m., said Capt. Mohammed Abdel Ghani.

The blasts highlight the constant danger posed by homemade bombs across Iraq, which have become the deadliest weapon used by mainly Sunni Arab insurgents against the US-led military presence in the country.

Three Marines were killed by a bomb blast Monday in Hit, 85 miles west of Baghdad, according to a statement.

The victims were assigned to the 22nd Marine Expeditionary Unit that has operated in Anbar province since mid-December with an Iraqi army battalion.

Another Marine, attached to the 2nd Marine Division, II Marine Expeditionary Force, died from wounds caused by a bomb blast Sunday in an unspecified location within Anbar, which includes the cities of Fallujah and Ramadi.

The latest deaths take the number of US military personnel killed to at least 2,257 since the Iraq war began in March 2003, according to an Associated Press count.

Early Tuesday, a roadside bomb struck a pickup truck south of Baghdad and killed two Iraqi civilians, while gunmen shot dead a supporter of fiery anti-US cleric Muqtada al-Sadr, police said.

The blast happened near a bridge in Youssifiyah, 12 miles south of Baghdad, and destroyed the vehicle the two people were travelling in, said Capt. Muthana Khaled. It was unclear if the civilians were the target of the attack.