UN spokesman Aleem Siddique said the United Nations would relocate about 600 of its 1,100 international staff in total.

Some will be moved to safer sites within Afghanistan while the rest will be withdrawn from the country.

He said: "The United Nations has been in Afghanistan for half a century and we are not about to leave now. The Afghan people want us to stay."

The figure was less than an earlier report that 900 international staff would be evacuated.

The UN statement said it would not make details of the new measures public, adding: "It is expected that they will involve short-term relocations for some staff while additional security is being put in place."