BAGHDAD -- A series of blasts rocked Iraq's northern city of Kirkuk on Sunday night, killing at least 11 people and wounding 50 others, a local police source told Xinhua.

At least seven explosions hit different parts of the city, among them a Shiite mosque and a local radio station, the source told Xinhua on condition of anonymity because he is not authorized to speak to the media.

"The latest report said?11 people were killed and 50 others wounded in the attacks," the source said. The death toll could further rise as some of the wounded were in serious conditions, he added.

The seven blasts were believed to be caused by car bombs, improvised explosive devices and mortars. Several buildings and a few civilian vehicles also suffered damage in the blasts.

Security forces have cordoned off the blast areas and tightened security measures for fear of fresh attacks, the source said. No one has so far claimed responsibility for the attacks.

Kirkuk, 250 km north of the capital Baghdad, is a major oil hub in north Iraq and sits atop some of the richest oilfields in the world. It is also part of the disputed territory between the central government and the semiautonomous region of Kurdistan. Violence has always been rife here since the 2003 Iraq war.

The oil-rich city has been the centre of contention for recent weeks. The central government established a new operation command to cover the disputed area, which angered the Kurdish regional government who later sent reinforcement troops to the area, causing a military confrontation. The tension was then defused by President Jalal Talabani under whose mediation the two sides agreed to withdraw troops.