A suicide bomber has detonated explosives in the middle of a crowd in the northern city of Konduz, killing at least 21 people and wounding at least 15 others.

Deputy police chief for Konduz Province Ghulam Mohammad Farhad said the bomber walked up to a group of riot police and set off the explosives.

Afghanistan's Shamshad TV reported that 20 of those killed were police and soldiers.

Police were out to maintain order at a demonstration in support of a local influential political figure accused of killing civilians.