In central Tikrit, US troops shot dead an Iraqi who they said had been shooting at them from a speeding car.
The driver of the car said they were not shooting at the troops but merely firing an AK-47 rifle in the air after celebrating at a wedding party.
A US soldier was killed and two others injured in a blast near the flashpoint Iraqi town of Ramadi, west of Baghdad. One of the injured soldiers later died of his wounds.
The three soldiers were in a convoy when the attack occurred around 6:30 am local time on Friday.
At least 197 US troops have been
killed in Iraq since 1 May
Resistance fighters also bombarded the occupation headquarters in Baghdad earlier on Friday, the first attack on the compound since US forces launched a large anti-resistance offensive in November.
The US military could not say what sort of weapons were fired at the 5 sq.km area, known as the Green Zone, on the banks of the Tigris river.
In another attack on a military convoy, south of Baghdad, a roadside bomb exploded wounding two Polish soldiers.
"We can confirm an attack against coalition forces. There was an explosion from an IED (improvised explosive device) and one Polish soldier is seriously wounded and one lightly wounded," a multinational force spokesman said on Friday.
"At 10:15 am (07:15 GMT) there was an explosion when a convoy went by," police Major Ibrahim Salam told AFP on the main road a couple of kilometres north of Hilla, and 100 kilometres from Baghdad.
A troop transporter, a Humvee all-terrain vehicle, two civilian cars and an Iraqi ambulance were halted on the roadside. A US helicopter flew in and out rapidly.
Occupation forces stopped anyone approaching the scene. An AFP correspondent travelling the same road reported a second blast shortly after against another Polish convoy a little further north.
Occupation forces on tenterhooks
The explosion went off between two vehicles and the convoy escaped with nothing worse than a burst tyre. Six more Polish military vehicles turned out to check the damage.
Poland, which deploys 2500 soldiers in Iraq, lost its first man in Iraq when a major was shot in the neck on 6 November.
The attacks followed overnight explosions in Baghdad late on Thursday which passed without casualties. Witnesses said the blasts took place inside the compound that hosts the US headquarters in the city.
Earlier on Thursday, one US soldier was killed and 14 others wounded when at least one bomber blew up a truck at an American army base outside Ramadi.
US military officials said the bomb was concealed in a furniture truck. The vehicle was driven by a bomber and it is believed that two other Iraqis in the truck also died in the explosion.