KABUL (Reuters) - An angry mob that killed seven foreign UN staff in north Afghanistan ripped out the door of a bunker where several had taken shelter, and slit the throat of one man who survived a bullet, the top UN envoy in the country said on Saturday.
Staffan de Mistura promised that the United Nations would stay in Afghanistan after the vicious assault, the deadliest it has faced in Afghanistan, but would have to reconsider security, particularly guarantees from Afghan forces.
He also warned that the Afghan government need to do more to prevent attacks like this if it wanted to keep the support of the international community as other nations face war and headline-grabbing unrest and absorb money and energy.
"We are not leaving," de Mistura told a small group of journalists in the Afghan capital, after flying back from Mazar-i-Sharif where he handled the aftermath of the attack.
Afghan police were the first line of protection on Friday when a crowd of up to 3,000 demonstrators enraged by the burning of a Koran by a militant fundamentalist Christian in the United States overran the compound, killing seven staff.
De Mistura said the violence, in a normally peaceful city, had caught ill-prepared Afghan police by surprise, and the gurkhas who are the next layer of security for the United Nations could not open fire because they are forbidden to shoot into crowds that contain civilians.
"Its clear if the Afghan police had a cordon of separation between the demonstration and the building, the building would not have been attacked," he said.
"The reality is that our gurkhas are never going to shoot at civilians, so the demonstration became an entry point, making it gradually impossible for our own gurkhas, our own security to intervene."
De Mistura said a small group of insurgents -- many from outside normally peaceful Mazar-i-Sharif city -- infiltrated a peaceful protest and turned it violent.
They were probably responsible for killing three civilian staff and four Ghurkhas, although a larger group had broken into the compound and hunted them down, he said.
All the Afghan national staff survived the attack, by blending into the crowd, and they heard unusual accents.
"We had our Afghan colleagues also, who all survived, they were not touched and they are able to detect a difference between the person of the street, of their own corner, of Mazar-i-Sharif, and a person who comes from outside."
"Those who were caught alive and arrested were actually indicating that kind of origin...I heard (they came from) five different locations, including Kapisa and Kandahar," he added.
Over 20 people have been detained over the violence.
STORMING THE BUNKER
The office was relatively empty because only a small group had gone into work on Friday, the Afghan weekend.
The four who were in the compound fled into the bunker when they heard the walls had been breached, but it had been built to withstand shrapnel from a bomb blast, not a sustained assault.
"The bunker is made for sustaining attacks by bombs, suicide bombers, not by a crowd of people with hammers or whatever they could find, so they were able to enter the door," de Mistura said.
When the attackers broke through the head of the mission, a Russian who spoke fluent Dari, stepped forward to try and draw attention to himself. He hoped three others cowering in darkness would not be noticed, but they were dragged out and killed.
"He tried to draw their attention on him, he hoped they would think there was no one else left," de Mistura said, adding that the mob went in with lamps and searched them out.
"One of my three colleagues was shot by a handgun and was wounded, and one of the infiltrators used a knife to kill him, but did not behead him," de Mistura said, responding to Afghan police reports that two staff members had been beheaded.
The Russian survived by claiming to be a Muslim.
The United Nations will review all its security procedures but also expects a stronger commitment from the Afghan government he said, warning that protecting foreigners working in the country was vital to guaranteeing international support.
"Afghanistan is not any more the center of the world, there is Tunisia, there is Libya, there is Egypt, there are other places which require and will require the attention of the international community, and taxpayers' money and of everyone else, energy," de Mistura said.
"So that means a further expectation of the Afghan side that there is a need of a special effort," he said, adding that corruption needed to be addressed alongside security.
(Editing by Andrew Marshall)