The explosion was caused by a suicide bomber ramming his explosives-laden car into a gate at the entrance to the airport.

The victims were all Afghans.

The Taliban took responsibility for the attack, saying it was a response to the burning of Muslim holy books at a US military base.

The bombing comes after nearly a week of deadly protests in Afghanistan over the matter.

An Afghan protester was killed and at least six US soldiers were injured on Sunday after a crowd of demonstrators attempted to force their way into a base in the northern province of Kunduz. The soldiers were injured after demonstrators threw hand grenades into the base, according to Afghan police.

At least 30 people are believed to have been killed in the violence as demonstrators continue to voice their anger over the Koran-burning incident.

On Sunday, Germany joined its close allies France and Britain in announcing that it was withdrawing its staff from Afghan ministries and agencies. German Development Minister Dirk Niebel, who announced the move, described it as "a strictly precautionary measure."

Afghan President Hamid Karzai renewed his calls for calm in a live televised address to the nation, saying the Koran burnings were being investigated.

"Now is the time to return to calm and not let our enemies use this situation," he said.

Karzai's words, though, appeared to have fallen on deaf ears.

The Afghan defense and interior ministers have cancelled trips to Washington to concentrate on the security concerns at home.

Meanwhile, Afghan police said they were still searching for "the main suspect" in the shooting of two US military advisers inside the Interior Ministry building in Kabul on Saturday. Taliban insurgents have claimed responsibility for the killings.

dfm, ncy/pfd (AFP, Reuters, DPA)