Police spokesman in northern city of Mazar-e-Sharif says demonstrators killed at least eight UN employees

The UN mission in Afghanistan has been thrown into a deep crisis after a furious mob of protesters killed and wounded a number of its staff in one of the country's most peaceful cities.

One police source in the northern city of Mazar-e-Sharif claimed at least eight foreign UN employees were killed after a demonstration in the thriving commercial hub turned violent. Other officials reported different figures.

Provincial police spokesman Sherjan Durrani said the demonstrators poured out of mosques in the city in the early afternoon, shortly after Friday prayers where worshippers had been angered by reports that a Florida pastor had burned a copy of the Qur'an.

Last year Terry Jones, a US fundamentalist Christian leader, did threaten to burn copies of the Muslim holy book. He backed down after warnings that Islamic opinion around the world could be inflamed and the lives of US troops in Afghanistan and Iraq endangered.

But on 21 March Wayne Sapp set light to a Qur'an with Jones standing by.

Durrani said that while most protesters were peaceful, others were seeking targets to attack, including shops and the UN compound.

Whatever the final death toll, the incident is seen as a disaster for the UN, coming just over a week after the Afghan president, Hamid Karzai, announced that Mazar-e-Sharif would be one of the first areas of the wartorn country to be transferred from Nato to Afghan government security control.

If the number of UN staff killed is high, the organisation will be obliged to consider closing down or dramatically reducing all its operations in the country – something it came perilously close to doing in late 2009 when an attack on a UN guesthouse in Kabul killed five staff.

The UN has already issued a "white city" order, which forces all staff in the country into lockdown in their compounds.

Earlier in the day hundreds of Afghans marched on the US embassy in Kabul.

In a statement the UN confirmed that some of its staff members had been killed. "The situation is still confusing and we are currently working to ascertain all the facts and take care of all our staff. The special representative of the secretary general, Staffan de Mistura, is on his way to Mazar-e-Sharif now to deal with the situation personally on the ground."