The US military says a car bomb attack near a hospital south of Baghdad killed 17 people and wounded 26 on Sunday.
US officials also said six American soldiers died in attacks south of Baghdad and north of the capital in Diyala and Salahuddin provinces. Earlier, the US military said a roadside bomb killed four American soldiers Saturday in Diyala province.
Meanwhile, thousands of Iraqis are gathering in Najaf for a protest Monday, on the fourth anniversary of the fall of Baghdad to U.S. forces. Radical Shi'ite cleric Moqtada al-Sadr urged Iraqis to protest the US presence in Iraq and demand that Iraqi security forces stop cooperating with the US military.
Iraqi military officials announced a 24-hour vehicle ban in Baghdad to try to curb violence on the anniversary.
Also Sunday, Iranian officials say they refused to allow a plane carrying Iraqi Prime Minister Nouri al-Maliki to fly through Iranian airspace on a trip to Japan, because permission was not requested in advance.
And, in Baghdad, military officials said a raid on a Sunni political party safe house netted a cache of weapons and bomb-making materials. Fourteen suspects were detained.