Spokesman Aleem Siddique said the UN would relocate about 600 of its roughly 1,100 international staff, with some being moved to safer sites within Afghanistan and the rest withdrawn from the country temporarily.

The UN said the evacuations would not disrupt its operations in the country. "We're doing everything we can to minimize disruption of our work during this period," UN special envoy to Afghanistan Kai Eide told reporters at a news conference in Kabul.

"We are simply doing what we have to do following the tragic events of last week to look after our workers in a difficult moment while ensuring that our operations in Afghanistan can continue."

The move, a week after five UN foreign staff were killed by militants in Kabul, complicates US President Obama's counter-insurgency war strategy, which foresees an influx of civilian assistance alongside extra troops.

Reuters