A clinic has been bombarded in the northern Afghan city of Kunduz, killing three MSF aid workers, with US forces investigating possible involvement.

The medical charity says 30 people were also unaccounted for. There is no word on the nationalities of the victims.

A US military statement said an air strike "may have resulted in collateral damage to a nearby medical facility".

The Taliban has clashed with government troops since its militants seized the northern city earlier this week.

Kunduz was the first major urban centre to fall to the Taliban in 14 years.

The medical clinic run by Medecins Sans Frontieres (MSF) was hit several times during "sustained bombing and was very badly damaged" at 02:10 local time (22:40 GMT) on Saturday, it said in a statement.

A spokesman for US forces in Afghanistan, Col Brian Tribus, said: "US forces conducted an air strike in Kunduz city at 02:15 (local time)... against individuals threatening the force.

"The strike may have resulted in collateral damage to a nearby medical facility."

The incident is being investigated, he added.

MSF director of operations Bart Janssens said: "We are deeply shocked by the attack, the killing of our staff and patients and the heavy toll it has inflicted on healthcare in Kunduz."

The charity says it does not have final figures. However, it says when the bombardment took place, there were more than 180 people in the clinic, including patients and staff.

It is the only medical facility of its kind in the north-east of Afghanistan.

Nato planes have been backing government efforts to retake Kunduz in recent days.

Many Taliban fighters have been pushed back to the outskirts, but fierce battles are continuing near the airport.

Afghan officials said the government had regained control of the city on Friday, but the Taliban denied the city had been retaken.

Kunduz, with a population of around 300,000, is one of Afghanistan's largest cities and strategically important both as a transport hub and a bread-basket for the region.

(BBC)