Afghan president Hamid Karzai has called on the US Congress to condemn the burning of the Koran by a militant American fundamentalist Christian pastor.

At least 18 people, including foreign United Nations workers, have been killed so far across Afghanistan in protests against the book burning.

In the most recent incidents, two policemen were killed and more than 30 people injured in the southern city of Kandahar.

Mr Karzai, who last week drew Afghan public attention to the burning, an event that initially gained little media coverage, called on the US Houses of Congress to join in the condemnation and prevent a repeat incident.

Mr Karzai made the request at a meeting with US ambassador Karl Eikenberry and General David Petraeus, his office said in a statement.

Mr Eikenberry read to Mr Karzai from US president Barack Obama's earlier condemnation of the Koran burning, the statement said. It gave no details of Mr Karzai's response.

Florida pastor Terry Jones supervised the burning of a Koran in front of about 50 people at a church in Florida on March 20.

Western political and military leaders, including Mr Obama and the top US and NATO commander in Afghanistan General Petraeus, have already condemned the act, as well as the violence that followed.

But their statements appear to have done little to placate anger across much of Afghan society.

On Sunday General Petraeus urged Afghans to understand that only a small number of people had been disrespectful to the Koran and Islam.

"We condemn, in particular, the action of an individual in the United States who recently burned the Holy Koran," General Petraeus said in a statement, which was also signed by NATO's senior civilian representative, ambassador Mark Sedwill.

Seven foreign UN staff and five Afghan protesters were killed on Friday after demonstrators overran an office in normally peaceful Mazar-i-Sharif city in the north.

A senior interior ministry investigator said on Sunday the killers of the UN staff appear to have been "reintegrated" Taliban - fighters who had formally laid down arms - although the insurgents have denied any role in the attack.

More than 30 people have been arrested, from areas as far afield as southern Kandahar, western Herat and central Baghlan province, said Munir Ahmad Farhad, a spokesman for the provincial governor.

With little sign of widespread anger fading, the governor also issued an order banning sermons which might "provoke the public." The violence in Mazar began after Friday prayers, some of them harshly critical of the West.

In Kandahar on Sunday, hundreds of people marched towards another UN office, again denouncing the actions of US preacher.

Around 1,000 people blocked the main highway from Kabul to Jalalabad earlier on Sunday and burned US flags.

"We want the preacher who burnt the Holy Koran to get a severe punishment," said 20-year-old protester Jalil Ahmad.

"He is not a human being, he is a brain-dead animal."

Mr Jones, a former hotel manager turned pastor who claims the Koran incites violence, has been unrepentant following the attacks and defiantly vowed to lead an anti-Islam protest outside the biggest mosque in the US on April 22.

The Taliban said in a statement on Sunday that Afghans were still ready to give their lives to protest against an offence that it said the West was not taking seriously.

ABC News