Fierce fighting erupted in the town of Buhruz northeast of Baghdad near Baquba after Iraqi fighters attacked a US patrol with small arms fire and rocket-propelled grenades early on Friday morning.
A US military spokesman later claimed that nine Iraqi fighters had been killed and three others wounded in the fighting.
Violence also flared in the northern city of Mosul when US forces tried to arrest what they said were Iraqi fighters holed up in a mosque.
Two US soldiers were wounded in clashes that followed. Another five soldiers were wounded when their convoy was hit by a roadside bomb as it left the area.
Shortly after another car bomb went off nearby killing one Iraqi and wounding another.
In Falluja, US warplanes and artillery targeted the al-Shuhada and Industrial neighbourhoods of the town.
A building used by US snipers also came under attack in central Ramadi, reported Aljazeera. Witnesses said the attackers used rocket propelled grenades.
US patrols were seen combing the area after the attack.
Medical sources also told Aljazeera that four Iraqis were killed when their car was hit by an explosive device that went off as a US military vehicle passed by in Alexandria area south of Baghdad.