Samarra is in Salahuddin province, where US and Iraqi forces have launched a series of operations against al-Qaeda in Iraq.
The fighters have regrouped there and in other northern provinces, after being pushed out of Baghdad and the western Iraqi province of Anbar.
Elsewhere in the country, seven Iraqi army soldiers and a major were killed in an ambush by anti-government fighters in the province of Diyala on Monday .
Brigadier-General Ragib al-Omairi, an Iraqi army commander based in Baquba, the provincial capital, said that armed men initially fired at an army patrol in the town of Bohruz.
|Security personnel are a favoured target of|
attacks by anti-government fighters [AFP]
"The two-car patrol came under fire ... rocket-propelled grenades and assault rifles [were used]," al-Omairi said.
"Major Salim Ghaluz and seven soldiers were among those killed."
Also on Diyala, police said on Monday that they found the decomposing bodies of eight women who had been blindfolded, handcuffed and shot in the head, in a grave in a town just north of Baquba.
And in Mosul, Iraq's third largest city, armed men killed four policemen in a drive-by shooting when they were on patrol in the city's east, police said.
More pilgrims killed
In other violence on Monday, four Shia pilgrims, three of them women, were killed and 15 more were wounded in south Baghdad.
The deaths were caused by a roadside attack in the Zafaraniya suburb as they headed to the shrine city of Karbala for the Arbain ceremony, medics and security officials said.
The previous day, at least 48 people were killed and 68 more wounded in a suicide blast blamed by US officials on al-Qaeda in Iraq.
The attacker detonated a vest filled with explosives at a rest stop for Shia pilgrims in Iskandariya, just south of Baghdad, hospital and security officials said.
The US military said on Sunday that they arrested four suspected al-Qaeda in Iraq leaders in Baghdad.
The four were reportedly involved in numerous recent operations in the area.
The military also said that a suicide bomber involved in an attack on Friday that killed five people outside a mosque in the city of Amiriya in Anbar province, appeared to be an "adolescent".