UN Assistance Mission in Afghanistan (UNAMA) has confirmed that three international staff working with the mission were killed, as well as four Nepalese Gurkha soldiers serving as guards at the operations centre. An unconfirmed number of Afghan demonstrators were killed. Many staff were also wounded, including the head of UNAMA's office in Mazar-i-Sharif.

Afghans chant anti-American slogans as smoke rises from a United Nations compound, during a demonstration to condemn the burning of a copy of the Muslim holy book by a U.S. pastor, in Mazar-i- Sharif April 1, 2011. [Xinhua]

The attack took place about 4:30 p.m. at an operations centre for the (UNAMA) in the northern city of Mazar-i-Sharif, according to information released by the mission.

A large crowd of demonstrators angry at the burning of a copy of the Koran by a United States group stormed a United Nations compound and killed a number of people, including three UN staff members.

Alain Le Roy, the Under-Secretary-General for Peacekeeping Operations, told reporters that the demonstration was one of several held across Afghanistan today in protest at last month's burning of a Koran by a Christian group based in the state of Florida.

He said many of the demonstrators in Mazar-i-Sharif were armed and, while the security guards tried their best, the crowd was so large that they were soon outnumbered.

The Security Council and Secretary-General Ban Ki-moon have strongly condemned Friday's attack in Afghanistan.

Mr. Ban described the attack as "outrageous and cowardly" and said it"cannot be justified under any circumstances."

In a statement the Secretary-General said those killed "were dedicated to the cause of peace in Afghanistan and to a better life for all Afghans. These brave men and women were working in the best tradition of the United Nations and gave their lives in the service of humanity."