The mortar was fired on Monday from an unknown source and blasted two cars on the main road north of Samarra, sources told Aljazeera.
In other developments, a US soldier was killed and two others wounded when a homemade bomb exploded in northern Iraq on Sunday, the US military said.
The attack happened south of the main northern city of Mosul, the military said in a statement on Monday which gave no further details.
Also, a US patrol came under mortar attack in Dhuliyyia area north of Baghdad. The US troops responded by opening fire on the attackers' position, injuring a passer-by and setting ablaze a farm in the area.
The eastern entrance of Falluja was the scene of intermittent clashes between US troops and armed resistance fighters, just prior to a raid by a US warplane on a house in the al-Askary neighbourhood of the city.
No further details were available on casualties in the clashes.
Also on Monday, the headquarters of the US troops in Baquba came under mortar attack. More than 20 explosions were heard inside the US base and heavy smoke was seen rising in the area.
Meanwhile, sources told Aljazeera that Husayn al-Saadi, head of the consultative council in the Iraqi southern city of Amara had survived an assassination attempt by unidentified people.
In another incident, Husayn al-Shami, chief of the Shia Endowment Diwan also survived a similar assassination attempt south of Baghdad.