"Ten (UN) people have been killed by the protesters. All the killed are foreigners," police spokesman Lal Mohammad Ahmadzai said.
"We are aware of an incident in our Mazar office, we are currently working to ascertain all the facts," said A spokesman for the UN mission in Kabul.
Afghanistan had condemned the "disrespectful and abhorrent" burning of the Quran by evangelical preacher Pastor Wayne Sapp in a Florida church, calling it an effort to incite tension between religions.
President Hamid Karzai called on the United States to bring those responsible for the burning of the Islamic holy book on March 21 to justice.
Sapp set light to a Quran under the supervision of Terry Jones, who last year drew condemnation over his aborted plan to burn a pile of the holy books to mark the anniversary of the September 11, 2001 attacks.
Jones cancelled his plans under enormous pressure from world leaders including US President Barack Obama, but the mere threat to burn the Muslim holy book sparked large protests in Afghanistan, where the UN and aid groups warned that civilians and aid workers in the country could be killed if the pastor went ahead.
Afghanistan is a deeply devout Islamic country where even rumours that the Quran has been insulted can result in deadly violence.
In January last year seven tribesmen were killed when Afghan security forces opened fire at demonstrations sparked by the alleged desecration of a Quran by US troops in the southern province of Helmand, a hotbed of insurgency.
The demonstrators were trying to overrun NATO bases and police facilities when they were fired on.
A subsequent investigation by NATO and Afghan authorities found that no Quran had been torched during an operation by the Western troops.
COMMENTS (3)
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ