A Taliban suicide car bomber targeting NATO troops at an airport in eastern Afghanistan killed nine people Monday, the seventh day of violence over the burning of the Koran at a US airbase.

The insurgents also said they were behind an attempt to poison foreign troops, as the death toll from unrest and protests that spread to even usually peaceful parts of the war-ravaged country hit about 40.

The UN announced that it was pulling its international staff out of their base in the northern Afghan province of Kunduz after it came under attack Saturday by demonstrators protesting the burning of the Koran.

The move came after NATO's International Security Assistance Force pulled all its staff out of Afghan ministries at the weekend when two US advisors were shot dead in the interior ministry, apparently by an Afghan colleague.

Six civilians, an Afghan soldier and two local guards were killed in the bomb attack on the military base at Jalalabad airport, but NATO troops escaped unhurt.

The Taliban said it was revenge for the Koran burning.

"The foreign forces have insulted our religion and this attack was revenge," Taliban spokesman Zabihullah Mujahid told AFP.

The hardliners also claimed that an "Afghan cook" working on their behalf poisoned the food of NATO troops at another base in the same province of Nangarhar.

NATO's International Security Assistance Force (ISAF) launched an investigation after "traces of bleach" were found in fruit and coffee, a spokesman said.

"There were no injuries, no fatality. The investigation is ongoing," said Master Sergeant Nicholas Conner.

On Sunday, seven US soldiers were wounded in a grenade attack during an anti-US demonstration at their base in northern Kunduz province, police said.

On Saturday, two US advisors were shot dead in the interior ministry in Kabul, just days after two US troops died as an Afghan soldier turned his weapon on them as thousands of demonstrators approached their base in the east.

The UN said the relocation of its international staff from the Kunduz base would be within Afghanistan.

It added it would "put in place additional arrangements and measures to make sure that the office can continue to operate in safety".

The US embassy has been in lockdown since the violence erupted and has warned of a "heightened potential threat to American citizens in Afghanistan".

Afghan President Hamid Karzai appealed on television for calm, while condemning the treatment of Islam's holy book.

In a televised weekend statement, he said he respected the emotions of Afghans upset by the Koran burning in an incinerator pit at Bagram airbase, but urged them not to let "the enemies of Afghanistan misuse their feelings".

Taliban insurgents have called on Afghans to kill foreign troops in revenge for the Koran incident and claimed to also have been behind the killing of the two US advisers in the interior ministry.

The shooting prompted NATO and several European countries to pull their advisors out of Afghan government ministries, while fallout from the Koran burnings widened as Afghan ministers cancelled a visit to Washington.

The Pentagon said Sunday that Afghanistan's defence and interior ministers had cancelled the trip this week to concentrate on addressing security concerns at home.

US President Barack Obama has apologised for the burning of the Korans, which officials said were inadvertently sent to the incinerator.