No one saw this coming. Not the UN, not Nato, not the Afghan police.
Mazar-e Sharif was the last place in Afghanistan where such an attack might have been expected.
The city usually has a bustling air about it. The local economy is thriving. It is usually quiet and calm. You might even see the odd tourist wandering around the famous Blue Mosque.
Outside the Blue Mosque yesterday, an imam began to harangue the crowd. Hundreds of Korans had been burned in the US, he said, not just one.
He was referring to events at a church in Florida on 20 March, when Pastor Wayne Sapp set light to a copy of the Koran. He was supervised by Pastor Terry Jones, who last year aborted a plan to burn copies of the Koran on the anniversary of the 9/11 attacks.
At the main Friday prayers in Mazar-e Sharif, the worshippers had been told to demonstrate.
But then it was the street sermon, outside, which seemed to inflame them.
What happened next is a matter of dispute. The provincial governor insists that the (so-far) peaceful protesters had not even intended to march on the UN until Taliban “infiltrators” diverted the crowd.
For some Afghan – and international — officials, this was a pre-planned attack, carried out by the Taliban, using the anti Koran-burning protest as cover.
The UN is not, so far, evacuating its personnel. The US military, for its part, is worried not just about Afghanistan but about many other Muslim countries where it has troops.
That is why General Petraeus, who is in charge of US forces in Afghanistan, personally appealed to Pastor Terry Jones last year not to burn a pile of Korans, as he had been threatening to do.
When the Koran was burned in a Florida church two weeks ago, there was little immediate reaction.
But news is getting out and spreading now and the fury – in Afghanistan – seems to be building.
Even if the Taliban did not orchestrate the events in Mazar-e Sharif, it may be strengthened by them.