Hundreds of people took to Afghanistan's streets Sunday in fresh protests against a Koran burning in the United States, as the UN vowed a deadly attack on its staff would not derail its work.
Demonstrations occurred in the main southern city of Kandahar as well as Jalalabad, in the east, officials said, as anger sparked by the burning of Islam's holy book spread.
On Friday seven staff at the UN mission in the usually quiet northern city of Mazar-i-Sharif were killed during a demonstration against the Koran burning and 10 other people were killed on Saturday in deadly protests in Kandahar.
The assault on the UN compound raises fresh concerns over plans by President Hamid Karzai and the international coalition to hand control of security in Mazar-i-Sharif, along with six other areas, to Afghan forces from July 1.
US President Barack Obama condemned the attack and also described the Koran burning at an evangelical church in Florida as an act of "extreme intolerance and bigotry".
Friday's attack on the UN was the worst in Afghanistan since the Taliban were toppled in 2001 but special representative Staffan de Mistura vowed the organisation's work would not be affected.
"This should not deter the UN presence, activities, in this country in this delicate and particularly crucial period," he said.
The remaining foreign staff from the compound, which was set ablaze in the mob attack, would be temporarily moved to Kabul, he said, but would return as soon as a secure office was established in Mazar-i-Sharif.
"This is not an evacuation. We will watch and monitor the situation everywhere in the country... and I will then decide on relocations inside the country -- not outside the country -- depending on the circumstances," he said.
De Mistura blamed insurgents from outside Mazar-i-Sharif for the deadly attack claimed by the Taliban, criticising police for failing to prevent the violence.
Giving the first full account of the attack, de Mistura said armed rebels had infiltrated street protests.
"Some insurgents, probably between seven and 15... had infiltrated the demonstration," de Mistura told reporters late Saturday in the capital Kabul.
He also criticised Afghan authorities, saying police should have thrown up a protective cordon around the building when the protest broke out.
Between 2,000 and 3,000 demonstrators had taken to the streets after the traditional Friday prayers.
The insurgents began throwing stones at the UN compound before storming it, and overwhelmed the guards, killing four.
"The police were not able to stop them and the (Nepalese) Gurkhas did not shoot at them -- the UN don't shoot at crowds, even if they are threatening -- and therefore they took over," he said.
De Mistura said the three Europeans -- a Swede, a Romanian and a Norwegian -- were shot after fleeing to a secure room within the compound, which the attackers succeeded in entering.
"What I reconstructed is... those who actually killed my colleagues were the infiltrators. They had handguns... and my colleagues were killed by handguns, all three of them. So I assume it was the infiltrators," he said.
One had his throat cut after being shot, he added.
The head of the UN office, a Russian, survived the attack by pretending to be Muslim and speaking the local language Dari.
While four guards died, two others escaped, as did two Afghan UN workers.
De Mistura said seven or eight people had been arrested over the attack, and some of them appeared to be rebels from elsewhere.
Friday's attack was the worst suffered by the world body since a bomb blast at the UN compound in Algiers in 2007 in which 17 staff died.
The Kandahar protests on Saturday began in the centre of the city and spread as police clashed with crowds marching towards the UN offices and provincial administration headquarters, witnesses said.
Kandahar is the spiritual heartland of the Taliban, who have fought an insurgency against Karzai's government and its Western allies since they were ousted by the US-led invasion.
Protesters gathered again on Sunday at three locations across the city shouting "Death to the US" and "Death to Karzai," witnesses and officials said.
In Jalalabad hundreds of students blocked a key highway leading to Kabul in similar protests, interior ministry spokesman Zemarai Bashary told AFP.
As well as condemning the Koran-burning, at the Dove World Outreach Center in Florida, Obama reiterated his condemnation of the "outrageous" attacks by protesters as "an affront to human decency and dignity."
De Mistura called the Koran burning an "insane and totally despicable gesture".