Baghdad, Iraq ? A suicide bomber detonated explosives Thursday inside a packed bus bound for a southern Shiite city, killing 32 people and wounding 44, police said. The blast pushed the three-day death toll from suicide attacks in the capital to at least 75.

The suicide attack occurred as the bus was pulling away from east Baghdad’s Nadhaa station bound for Nasiriyah, 200 miles to the south. A man carrying a bag suddenly jumped on the vehicle through the open door, apparently waiting until the last moment to board to avoid security checks.

He was challenged by the conductor but insisted on taking a seat, police Lt. Wisam Hakim said.

“He sat in the middle of the bus and then the explosion took place,” Hakim said.

Police Lt. Ali Mitaab said 32 people were killed and 44 wounded. Most of those killed were on the bus, which was gutted by flames, but several people around a food stall also died, police said.

Officials at the scene said the death toll was especially high because the blast triggered secondary explosions in gas cylinders at the stall.

Several other explosions occurred Thursday morning, including one that struck an American convoy and killed a U.S. soldier, the military said. The U.S. command also said a Marine was killed the day before in a bombing in Ramadi, 70 miles west of Baghdad.

An Iraqi soldier inspects the site of a suicide attack in a bus station in Baghdad. A suicide bomber detonated an explosive belt Thursday in a bus as it was about to depart for a Shiite city in the south, killing at least 32 people and wounding 44, police said.

The bus attack occurred two days after a pair of suicide attackers killed 43 people and wounded more than 70 at Baghdad’s police training academy.