Unknown gunmen have attacked a United Nations police base in the Malian city of Timbuktu, the UN said, while security sources said a Malian army checkpoint in the city had also come under fire.

Olivier Salgado, spokesman for the UN peacekeeping mission in Mali (MINUSMA), told Al Jazeera the assailants launched the attack after they detonated a car bomb at the base at 6:30am on Friday.

He said one policeman was slightly wounded in the assault, and the attackers remained holed up inside the base.

Malian and MINUSMA forces were still engaged in a gunfight, Salgado said. The base was already in the process of being relocated, he added, meaning only about 20 police officers were there at the time.

A military source in Timbuktu told Reuters news agency that the UN site, near the entrance to the city, had been taken over exclusively by a Nigerian police contingent.

Simultaneously, a Malian army checkpoint in the Kabara neighbourhood near the airport was attacked by gunmen. It was not immediately clear if there were any casualties.

Armed groups, who briefly held the city of Timbuktu in 2012 until French forces drove them out, have stepped up attacks in Mali in recent months as part of a growing regional insurgency.

In November, a breakaway al-Qaeda faction from the country's troubled north, al-Mourabitoun, claimed responsibility for a brazen attack on a five-star hotel that killed 21 people in the heart of the capital, Bamako.

Last month, al-Qaeda fighters seized a Swiss missionary living there and set conditions for her release.