At least 18 people have been killed in suicide bomb attacks in two cities north of the Iraqi capital, Baghdad, officials said.

One bomber detonated an explosives-rigged vehicle at the southern entrance to Tikrit, while the other blew up an ambulance in Samarra.

Ten Iranian pilgrims were killed in the blast in Samarra, the Iranian news agency ISNA quoted an Iranian official as saying.

The official said the Iranians were getting off a bus when an ambulance carrying the suicide bomber approached them and blew up.