Another suicide bomber blew himself up in a central Baghdad hotel, killing seven people, police said.
At least 12 other people were reported wounded.
A man wearing a belt of explosives walked into the lobby of the Mansour Hotel, approached the reception desk and detonated his bomb, said a police official.
The high-rise hotel, on the banks of the Tigris River, houses the Chinese Embassy and the news agency Agence France-Presse, among other tenants.
Also on Monday, a suicide car bomber blew himself up at a checkpoint in Hillah, the capital of Babil province, killing at least eight people and leaving 31 wounded.
The bomber drove his car into a checkpoint close to the headquarters of the provincial government before detonating himself.
A police spokesman said the eight killed included three policemen and at least four officers were among the wounded.
The blast damaged the concrete walls that surround the main building and shattered glass, but relatively few people were in the area because of the early hour, the spokesman said.
It was the second attack in the predominantly Shia city in three days, after a parked car packed with explosives blew up on Saturday in the center of the city.
Two US soldiers were killed Monday in separate attacks in the Baghdad area, the military said.
A roadside bomb killed one soldier and wounded three others when it exploded near a US vehicle during combat operations in an eastern section of the capital, according to a statement.
The US command also reported a US soldier killed in a small-arms attack on Monday in an unspecified location in south Baghdad or its outskirts.
The deaths raised to at least 3,561 members of the US military who have died since the Iraq war started in March 2003, according to an Associated Press count.
Meanwhile, the US military said it has uncovered an "execution house" in the city of Baquba, northeast of Baghdad.
US and Iraqi forces "discovered the execution house using information from local citizens, who said it had been used by al-Qaeda," a US military statement said.
"Soldiers searching the house found five bodies buried in the yard behind the building and bloody clothes in several rooms inside it."
The announcement comes on the sixth day of a major air and ground assault by US and Iraqi forces on Baquba, which US commanders say has long been a stronghold for al-Qaeda in Iraq.