MAZAR-e-SHARIF, Afghanistan — Stirred up by a trio of angry mullahs who urged them to avenge the burning of a Quran at a Florida church, thousands of protesters overran the compound of the United Nations in this northern Afghan city Friday, killing at least 12 people, Afghan and U.N. officials said.

The dead included at least seven U.N. workers - four Nepalese guards and three Europeans from Romania, Sweden and Norway - according to U.N. officials in New York. One was a woman. Early reports, later denied by Afghan officials, said that at least two of the dead had been beheaded. Five Afghans were also killed.

The attack was the deadliest for the United Nations in Afghanistan since 11 people were killed in 2009, when Taliban suicide bombers invaded a guesthouse in Kabul. It also underscored the latent hostility toward the nine-year foreign presence here, even in a city long considered to be among the safest in Afghanistan - so safe that U.S. troops no longer patrol here in any numbers.

Unable to find Americans on whom to vent their anger, the mob turned instead on the next-best symbol of Western intrusion - the nearby U.N. headquarters.

"Some of our colleagues were just hunted down," said a spokesman for the U.N. Assistance Mission in Afghanistan, Kieran Dwyer, in confirming the attack.

In Washington, President Barack Obama issued a statement strongly condemning the violence against U.N. workers.

"Their work is essential to building a stronger Afghanistan for the benefit of all its citizens," he said. "We stress the importance of calm and urge all parties to reject violence."

The statement made no reference to the Florida church or the burning of the Quran.

Reacting with violence

Afghanistan, deeply religious and reflexively volatile, has long been one of the most reactive flashpoints to perceived insults against Islam. When a Danish cartoonist lampooned the Prophet Muhammad, four people were killed in riots in Afghanistan within days in 2006. The year before, a one-paragraph item in Newsweek alleging that guards at Guantanamo Bay, Cuba, had flushed a Quran down the toilet set off three days of riots that left 14 people dead in Afghanistan.

Friday's episode began when three mullahs, addressing worshipers at Friday Prayer inside the Blue Mosque here, one of Afghanistan's holiest places, urged people to take to the streets to agitate for the arrest of Terry Jones, the Florida pastor who oversaw the burning of a Quran on March 20.

Otherwise, said the most prominent of them, Mullah Mohammed Shah Adeli, Afghanistan should cut off relations with the United States.

"Burning the Quran is an insult to Islam, and those who committed it should be punished," he said.

The crowd - some of its members carrying signs reading "Down with America" and "Death to Obama" - poured into the streets and swelled. Gov. Atta Muhammad Noor of Balkh province, of which Mazar-eSharif is the capital, later put the number at 20,000. According to Lal Mohammad Ahmadzai, spokesman for Gen. Daoud Daoud, the Afghan National Police commander for the country's north, the crowd soon overwhelmed the U.N. guards, disarming some and beating and shooting others.

Gen. Abdul Rauf Taj, thé deputy police commander for Balkh province, put the death toll at eight foreign U.N. staff members, but he said there had not been any beheadings.

"Police tried to stop them, but protesters began stoning the building, and finally the situation got out of control," he said.

Ahmadzai, however, put the death toll at 10 foreigners in the U.N. compound, eight killed by gunshots and two beheaded.

Dwyer confirmed that some U.N. staff members had been killed, but he declined to provide a number or the nationalities of the victims until next of kin had been notified.

Mirwais Rabi, director of the public health hospital in Mazar-e-Sharif, said 20 wounded and five dead Afghan civilians were brought to the hospital in all.

Weapons taken from guards

The mob also burned down part of the U.N. compound, toppled guard towers and heaved blocks of cement down from the walls. The victims were killed by weapons that the demonstrators had wrestled away from the U.N. guards, Noor said.

He listed the dead as five Nepalese guards and two Europeans, a breakdown that varied from the one issued later by Farhan Haq, the deputy U.N. spokesman in New York.

Noor also blamed what he said were Taliban infiltrators among the crowd for urging violence and even distributing weapons; he said 27 suspects were arrested on charges of inciting violence.

Jones, the Florida pastor, caused an international uproar by threatening to burn the Quran last year on the anniversary of the terror attacks of Sept. 11, 2001. Among others, the overall commander of forces in Afghanistan, Gen. David H. Petraeus, had warned at that time that such an action could provoke violence in Afghanistan and could endanger U.S. troops.

Jones subsequently promised not to burn a Quran, but he presided over a mock trial and then the burning of the Quran at his small church in Gainesville, Fla., on March 20.

Last week, President Asif Ali Zardari of Pakistan condemned the burning in an address before Parliament, and President Hamid Karzai of Afghanistan on Thursday called on the United States to bring those responsible for the Quran burning to justice.

A prominent Afghan cleric, Mullah Qyamudin Kashaf, the acting head of the influential Ulema Council of Afghanistan and a Karzai appointee, also called for U.S. authorities to arrest and try Jones in the Quran burning.

The Ulema Council recently met to discuss the Quran burning, Mullah Kashaf said in a telephone interview.

Jones was unrepentant.

"We must hold these countries and people accountable for what they have done as well as for any excuses they may use to promote their terrorist activities," he said in a statement. "Islam is not a religion of peace. It is time that we call these people to accountability."