In one incident, a US Marine was killed and two wounded on in an attack on their convoy east of Falluja, a US occupation military spokesman said.
He said fighters exploded a bomb close to the convoy and then fired rocket propelled grenades and small arms.
In the other incident, one US soldier was killed and two others wounded when a bomb was detonated near their patrol in Baquba, 65 km north of Baghdad.
Another US soldier was killed in an attack on a convoy near Taji, about 40 km north of Baghdad, on Wednesday, US military officials confirmed.
The attacks brought to 398 the number of US soldiers killed in hostile action since the start of the war.
On Wednesday, a suspected rocket attack on a Baghdad hotel used by foreign contractors and journalists triggered a huge blast, but no injuries were reported.
"There's evidence of some sort of rocket hitting the hotel at about the sixth floor," said one guest at the Ishtar Sheraton hotel on Wednesday.
The explosion shattered windows, smashed concrete and shook people from their beds inside the hotel and in nearby neighbourhoods. Iraqi police and the US military set up a cordon outside the building.
The Sheraton and the adjacent Palestine hotel, both situated in a well-defended complex used by foreigners in the heart of the city, have been attacked several times in the past.
Eleven policemen were killed on
Tuesday by resistance fighters
Earlier in the day, a foreign security guard and an Iraqi child were killed in a drive-by-shooting outside the restive city of Falluja, 50km west of Baghdad, a US army spokesman said.
"One foreign protective security personnel and one child were killed in a small arms fire attack near to Falluja at approximately 7:30pm to 8:00pm (16:30 GMT to 17:00 GMT) on Tuesday," the spokesman said.
The attack was a drive-by-shooting, according to the spokesman, who added that no occupation forces were hurt. He was unable to give the nationality of the dead foreigner.
Also in Falluja, three Iraqis were killed and two US troops wounded when the soldiers came under attack.
"The bodies of three people were brought into our establishment and three others with injuries were admitted," said Muthanna Khudair, a doctor at the main hospital in Fallujah, 50km west of Baghdad.
Meanwhile in Mosul, three Iraqi policemen were wounded in an explosion in the northern city of Mosul on Wednesday, police officer Abd Al-Azil Hazim Hafuzi said.
An unidentified device exploded as a police pick-up truck drove by in central Mosul, injuring its three passengers, the officer said. The casualties were taken to hospital.