Afghanistan has been hit by more violent protests against the burning of a Koran in the US, a day after seven UN workers were brutally murdered.
At least nine people are thought to have died in the latest demonstrations in Kandahar, as crowds surged through the streets chanting "Death to America".
Foreign Secretary William Hague has added his voice to condemnation of the "brutal" attack on the UN compound in Mazar-e-Sharif yesterday.
The international body's staff remain on maximum security alert, but have not been evacuated.
Rawof Taj, deputy police chief in Balkh province, said the mastermind was one of more than 20 people arrested after the incident.
However, the Taliban rejected claims that it was responsible, saying it had been a spontaneous reaction to an "insult".
The Norwegian Defence Ministry named one of the victims as Lt Col Siri Skare, a 53-year-old female pilot.
A Swede and four UN guards from Nepal were also killed, and a Romanian citizen is also said to have died.
It is not believed that any of the dead were British.
UN secretary-general Ban Ki-moon, in Nairobi, Kenya, said: "This was an outrageous and cowardly attack against UN staff which cannot be justified under any circumstances and I condemn in the strongest possible terms."
US President Barack Obama also condemned the incident and underscored the importance of the UN's work in Afghanistan.
"We stress the importance of calm and urge all parties to reject violence and resolve differences through dialogue," he said.
Mr Hague said: "The families and friends of those killed have my deepest sympathies. The work of the United Nations Assistance Mission in Afghanistan is of utmost importance.
"It is vital that they can carry out their work in a safe and secure environment."
The protesters gathered outside the UN compound yesterday in response to the reported burning of the Koran at the Rev Terry Jones's church, the Dove Outreach Centre, in Gainesville, Florida.
The march turned violent when demonstrators grabbed weapons from the UN guards and opened fire on the police, then stormed the building.
Pastor Jones, who previously sparked outrage by announcing plans to burn copies of the Koran to mark the anniversary of the 9/11 attacks, told the BBC he was "absolutely not responsible" for yesterday's atrocities.
Instead he launched another broadside against Islam, saying: "We must take a serious, serious look at Islam.
"It's a violent religion that promotes acts of violence, I believe we need to bring this before the UN."Reuse content