Afghan protesters angered by the desecration of Quran by an obscure US pastor killed up to 20 UN staff, beheading two foreigners, when they overran a compound in a normally peaceful northern city on Friday in the worst ever attack on the UN in Afghanistan.

At least eight foreigners were among the dead after attackers took out security guards, burnt parts of the compound and climbed up blast walls to topple a guard tower, said Lal Mohammad Ahmadzai, a police spokesman for the northern region. A police source said the chief of the mission in the city was wounded but survived.

Five protesters were also killed and around 20 wounded.

The governor of Balkh province said insurgents had used the march as cover to attack the compound, in a battle that raged for several hours and raises serious questions about plans to make the city a pilot for security transfer to national forces.

An AFP reporter in Mazar-i-Sharif said the violence continued for three and a half hours, with small arms fire and explosions heard. There were about 500 protesters, the correspondent said. “The protesters made a resolution containing 13 items which asked the foreign troops to leave Afghanistan, stop killing of civilians, and untie all diplomatic relations with the United States government,” he said.

“The insurgents have taken advantage of the situation to attack the UN compound,” said Governor Ata Mohammad Noor.

He told a news conference that many in the crowd of protesters had been carrying guns. Some 27 people have already been detained over the attack, he added. Friday’s attack followed a protest march led by religious clerics and attended by around 200 in Kabul on Friday against the Quran desecration and plans announced by Karzai in February for possible permanent US bases in Afghanistan.

The demonstrators, who left from mosques in downtown Kabul after Friday prayers, burned a US flag and stamped on it, shouting ‘Death to America’.