An AFP correspondent in the city said powerful explosions rocked Samarra's northern edge near al-Qadisiya neighbourhood starting at about 7pm (1700 GMT) on Tuesday, and mosques later urged residents to donate blood.
The area has been the scene of sporadic deadly clashes since a powerful car bomb attack on 8 July on the city's Iraqi National Guard headquarters killed five US soldiers and four Iraqi guardsmen.
US soldiers at an observation post in northern Samarra said they were attacked at 7.30pm (1530 GMT) with mortar rounds and small arms fire from a house and a mosque.
"Two tanks protecting the observation post returned fire on the house and destroyed it," the military said in a statement late on Tuesday.
"Aerial observation was called in to help ground troops locate anti-Iraqi (sic) forces who were firing on them," it said, adding that troops later came under fire from various locations including two other houses.
An Iraqi man salvages personal
items from his destroyed home
The army added it called in "close air support" starting at about 9.30pm (1730 GMT) and that the battle was still ongoing.
In other developments, the mutilated body of an Iraqi scientist and an unidentified corpse were found in Samarra.
"Two bodies were found at 3.30am (2330 GMT on Tuesday) in Samarra," said Major Sadun al-Dalami, chief of police at the general hospital in the city, 125km north of Baghdad.
The first, identified as doctor Basim al-Mudris, an employee at a local drugs company who had a Phd in chemistry, was found near a mosque in the southern al-Jubaliya district.
"It looked as though he had been tortured as his body was mutilated," Dalami said, adding that the second corpse was discovered in the east of Samarra.
In further unrest in the north of the country, one policeman was killed and four were wounded when their patrol was targeted by rocket-propelled grenade fire.
Iraq's security services were again under attack in the oil-rich city of Kirkuk, 225km north of Baghdad.
Attackers opened fire on a police patrol killing one policeman and injuring four, three of them seriously, said Lieutenant Husayn Allawi, chief of al-Aruba police station in the eastern side of the city.
"One of the police station's patrols was attacked by a rocket propelled grenade when it was crossing Grenada bridge," he said, adding the wounded had been taken to hospital.