A roadside bomb ripped through a US military convoy north of Baghdad, killing three soldiers.
A military vehicle was destroyed in the blast that occurred at around 9 am (06:00 GMT) near the town of Samarra, 100 km north of Baghdad, a US military statement said.
In the northern city of Arbil, four people were killed and 20 others injured in a car bomb explosion, our correspondent reported.
The explosion took place at the entrance of the Interior Ministry headquarters at 08:50 GMT, setting the building ablaze and killing the security guards.
The blast also shattered the windows of nearby residential buildings.
The cause of the explosion was not immediately known.
The police cordoned off the area.
In the third incident, one person was killed and four, including a child, were injured when a landmine exploded underneath a car, near al-Shurta flyover in Baghdad, the correspondent reported.
In north Iraq's Rawa city, US occupation forces have arrested about 80 people, the correspondent reported.
Iraqis face the brunt of
Our correspondent was prevented by the forces from entering the city.
While some of the arrested people were former Baathists, others belonged to the Iraqi Islamic party, people coming out of Rawa said.
The forces have even arrested old men and youngsters, they added. The arms confiscated were only light weapons, usually found in every Iraqi house.
Some of those who were arrested had their faces covered due to the cold weather. But the occupation forces thought they were resistance fighters, the correspondent added, quoting the locals.
After the arrests, the forces pulled out of Rawa.
Baghdad bombingMeanwhile, US aircraft and artillery units blasted suspected rebel hideouts in Baghdad overnight.
Dozens of explosions were heard across the city in one of Baghdad's heaviest bombardments since the end of the US-led war.
Captain Jason Beck, spokesman for the First Armoured Division that controls Baghdad, said Operation Iron Force was aimed at rebels who might use the holiday season to step up attacks.
"The purpose of the operation is to attack, kill or capture individuals (launching attacks) against coalition activities," Beck said.
"Enemies will use the holidays to attack for psychological reasons. This is obviously a special time of the year for all soldiers, so we must remain vigilant."
Raids to continue
Beck said the US operation focused on areas of Baghdad where "the enemy has launched attacks on coalition forces before".
"This is obviously a special time of the year for all soldiers, so we must remain vigilant"
Captain Jason Beck,
spokesman, First Armoured Division
He said the targets were "based primarily on intelligence from various sources, one of these sources is the individuals
captured as a result of Saddam Hussein being captured".
Local people said fields used by fighters to attack US patrols in southern Baghdad were heavily bombed.
Beck said it was too early for "battle damage assessments", but vowed to continue the operation.
"Operation Iron Force will remain until the enemy is destroyed or surrenders," he said.