The latest deaths on Wednesday raised to at least 30 the number of US soldiers who have died this month.
The US military also said two US soldiers were killed in Baghdad on Sunday and a navy sailor was killed in Anbar province on Monday.
At least 69 troops were killed in November and 105 soldiers were killed in October - the highest amount for a month since January 2005.
At least 2,918 service members have been killed since the war started in 2003, according to the Associated Press news agency.
Mortar attacks
At least eight people were killed and dozens wounded after a series of mortar bombs exploded in a busy commercial district of Baghdad, in other incidents on Wednesday.
The mortar attacks, which took place in a central market and the southern town of Suwayra, came on the day at least 75 Iraqis were killed or found dead across the country, including 48 whose bullet-riddled bodies were found in different parts of the capital.
Elsewhere, two people were killed when a suicide bomber blew himself up on a minibus travelling through the predominantly Shia, Sadr City, Thaer Mahmoud, a police spokesman said. Another 15 were wounded in the attack.
A bomb also exploded in the town of Iskandariya, south of Baghdad, killing four, police said.
In a western Baghdad district, armed men attempted to assassinate Brigadier-General Mohsen Qassim, the head of the security force of Iraq's Sunni-controlled ministry of higher education, but only killed his driver.
Bus ambushed
Wednesday's violence follows the killing of 30 people in central Baghdad on Tuesday.
Armed men killed 14 employees of a Shia religious foundation in the Iraqi capital, while three car bombs killed 16 people in a separate attack near a petrol station in a religiously mixed area.
The employees of the Shia foundation were killed when their bus was ambushed, Salah Abdul Razzaq, a spokesman for the organisation said.
Interior ministry sources said the attackers first set off a car bomb and then sprayed the bus with bullets on a highway in northern Baghdad.
Three car bombs were detonated in sequence in the attack on the petrol station in southwest Baghdad.
The explosions occurred in Biyaa, a mixed Sunni Arab and Shia section of the city.
