NATO chief Anders Fogh Rasmussen insisted trust had not broken down between alliance-led troops and Afghan security forces, despite incidents in which Afghans turned their weapons on their American partners.

The assaults did "not represent the full picture of the daily cooperation" between the NATO-led International Security Assistance Force (ISAF) and Afghan troops, he told reporters during a visit to Washington.

"I deplore the violence we have seen during the last week. But across the country ISAF troops are showing great restraint and professionalism. And Afghan security forces have shown considerable courage in their effort to minimize the violence," he said.

Two US military advisers were gunned down in the interior ministry in Kabul on Saturday, days after two American troops were killed by an Afghan soldier in the east. On Sunday, seven US soldiers were wounded in a grenade attack during an anti-US demonstration in northern Kunduz province.

NATO promptly pulled its military advisers out of Afghan government ministries following the shooting over the weekend.

Popular outrage erupted after Afghans learned that copies of the Koran were brought to an incinerator at the US-run Bagram airbase. Top US and NATO officers have apologized and insisted the incident was a grave error but not intentional.

Rasmussen accused Islamist insurgents of attempting to exploit anger over the Koran burning and said he hoped that NATO military advisers would soon return to their posts at Afghan government ministries.

"The enemies of Afghanistan will not succeed in dividing us from our partners. We want to resume with the close cooperation as soon as possible," he said.

"But of course we also have to take the necessary measures to ensure our people can do their work in a secure environment."

Echoing comments by US officials on Monday, Rasmussen said the turmoil would not trigger any change in the alliance's timeline for a gradual troop withdrawal and handover to Afghan forces by the end of 2014.

NATO has a 130,000-strong US-led military force fighting the Taliban, which has led an insurgency against the Western-backed Kabul government since being toppled from power in 2001.

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".

But despite the continuing violence, the US military said it has no plans to alter its troop drawdown timetable in Afghanistan.

"We're not going to let the events of the past week, which are regrettable and unfortunate and tragic, influence the long-horizon view that we're taking with respect to... Afghanistan," said Pentagon spokesman George Little.

The US, he said, has an "unwavering" commitment to hand over to Afghan security forces by the end of 2014 as agreed by NATO.

Meanwhile, 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.