Insurgents struck at least three times in Iraq on Wednesday, killing US troops in Samarra and Iraqis in Irbil.
US soldiers continue to come under attack
Separately, a missile was fired at a hotel used by Westerners in Baghdad, apparently causing no casualties.
Churches in Baghdad called off the traditional Christmas Eve midnight Mass in response to the security situation in the country.
The churches held daytime services because of the risks of moving around the Iraqi capital at night.
The three US troops were killed by a roadside bomb as their convoy passed near the town of Samarra in the Sunni triangle.
The attack happened in the area known as the Sunni triangle, where insurgents have often launched attacks on US troops.
The BBC's Chris Hogg in Baghdad says the improvised devices have proved a simple yet effective weapons against US-led forces in Iraq.
Two American soldiers were killed in a similar bombing on Tuesday.
The latest attack brings to 205 the number of US soldiers killed since President Bush declared an end to major combat operations in May.
The Irbil bomb exploded outside interior ministry offices, killing a suicide bomber and at least four other people - two of them policemen guarding the building.
The blast damaged the ministry and shattered windows in nearby buildings.
The Kurdish north has been the most stable region of Iraq since US-led forces ousted Saddam Hussein in April.
The missile aimed at Baghdad's Sheraton hotel may have hit the upper floors of the building, but US military sources say there were no casualties.
The hotel was the target of attacks a month ago, when assailants fired rockets from a donkey cart at it and the nearby Palestine hotel.
Two people were injured in that attack, in which a fifth-floor atrium roof above the reception area was destroyed.
The hotel's guests include Western journalists and contractors working on the rebuilding of Iraq.
The hotel came under attack a month ago
The BBC's Orla Guerin says Wednesday's explosion happened after attackers fired a missile towards the hotel from a nearby street.
There is an elaborate network of security checks involving concrete barriers and metal detectors around the hotel, she says.
But she says the defences focus on only one side of the hotel, leaving other sides less well guarded.
US forces have warned of the possibility of attacks from those who oppose the US occupation of Iraq as Christmas approaches.