A suicide bomber tore through a crowd of Afghan demonstrators under a heavy police presence on Monday, killing 16 people in the northern city of Kunduz.

A suicide bomber tore through a crowd of Afghan demonstrators under a heavy police presence on Monday, killing 16 people in the northern city of Kunduz, officials said.

The attack took place in the main square of the city. However, reports of the death toll varied.

Police said 15 people were killed, both civilians and police, with Lal Mohammad Ahmadzai, the police spokesman for northern Afghanistan, said seven policemen and eight civilians were killed.

Local residents said that people had been gathering for a demonstration connected to the recent killing of civilians and that there had been a strong police presence.

There was no immediate claim of responsibility but similar attacks in the past have been blamed on the Taliban and their extremist allies fighting for 10 years to overthrow the Western-backed government and evict NATO troops.

The attack comes just two days after a suicide bomber, whom police identified as a teenager, blew himself up outside NATO occupation headquarters in Kabul, killing six youngsters aged 12 to 17.

Last month, a bomb attached to a motorcycle killed 11 people in a market elsewhere in the province, in Archi district near the border with Tajikistan.

Earlier on Monday, the United States formally handed control to Afghanistan of more than 3,000 detainees at Bagram prison, as part of NATO plans to hand over national security to Afghans and withdraw its combat troops by the end of 2014.

The United Nations says 1,145 civilians were killed in the war in the first six months of this year.