The agencies said the American State Department was not specific about the danger but said there were threats to non-Muslim aid workers.

BBC Afghanistan Correspondent Pam O'Toole says it is not clear if the perceived danger is linked to speculation that Washington may be about to mount an attempt to seize Saudi dissident Osama bin Laden, who is living in Afghanistan.

Mr bin Laden is regarded as a suspect in the recent bombings of American embassies in Africa.

He has denied any involvement in that attack, but has told the BBC he would continue his war against the Americans and the Jews.

In the wake of the Africa bombings the US evacuated non-essential personnel and their relatives from its embassy in Pakistan because of what it called a very serious threat to Americans.

Taleban refuse to hand over suspect

The Taleban movement, which controls much of Afghanistan, has ruled out the possibility of handing over Mr bin Laden to the US Government in return for recognition by Washington.

Osama bin Laden: Taleban say he is innocent

The founder of the Taleban, Mullah Mohammed Omar, said that the Saudi dissident could not have been not involved with the attacks as did not have the power or the resources to explode bombs in Africa.

However, the Washington Post has reported Pakistani intelligence sources as saying that a suspect extradited to Kenya, Mohammed Sadiq Howaida, confessed he was involved in the bombings and said Osama bin Laden sponsored and financed the operation.

The row comes amid growing tension between aid agencies and the Taleban.

Aid sources say the atmosphere has become increasing tense in recent weeks, as the Taleban have consolidated their hold over most of the country.

Russian concern

Meanwhile, Russia and Tajikistan have again voiced their concern over the fighting in northern Afghanistan.