Afghan officials said at least twelve people have been killed at a UN operational centre in the northern city of Mazar-i-Sharif when protest against the burning of the Quran turned violent.

Demonstrators stormed the UN office Friday, opening fire on guards and setting fires inside the compound after reports that an evangelical pastor burned a copy of the Muslim holy book in Florida in March.
At least eight foreigners and four Afghan protesters have been killed when the demonstration turned violent. An estimated 20 other demonstrators were injured.
Two of the UN staff members were beheaded, according to police.
Al Jazeera's Hashem Ahelbarra reported from Kabul that people converged outside the UN mission soon after the midday prayers.
The mission is one of the backbones of UN operations in the country, he said. Some of the protesters were armed with knives, and the chief of the mission was badly injured in the attack.
""The protests degenerated into a very violent attack,"" he explained.
Afghan officials said about 2,000 people peacefully gathered outside the UN office in the northern city of Mazar-i-Sharif, until some protesters grabbed weapons from the UN guards, opened fire on the police and stormed the building.
Farhan Haq, a spokesperson for the UN Secretary General Ban Ki-moon, spoke with Al Jazeera from New York.
Ban is seeking more information on the attack, and considers it ""a cowardly attack which no circumstances could justify,"" Haq said on Friday.
Stephane de Mastura, the head of the UN's mission to Afghanistan, was travelling to Mazar-i-Sharif on Friday to investigate what had happened, he added.
The UN staff in Mazar-i-Sharif worked in a range of areas, including electoral support, political advice, humanitarian aid, reconstruction and development.
""All of this is designed to provide as much assistance as possible to the Afghan people, which is what makes it so unjustified that this office was attacked,"" the spokesperson said.
Daud Daud, commander of Afghan National Police in the north, said five Nepalese guards were amongst those killed. The guards worked for a private security firm.
The UN has not yet announced the nationalities of the other three foreigners who were killed.
Terry Jones, an American pastor, created a storm of controversy after he announced that he would burn copies of the Quran on the anniversary of the September 11 attacks last year. Under pressure from political leaders, Jones ""suspended"" the event.
However, on March 20, Jones oversaw the burning of a copy of the Muslim holy book by another pastor, Wayne Sapp.
Source: Al Jazeera and agencies