UNITED NATIONS - The number of refugees fleeing Afghanistan could grow exponentially as the U.S.-led war against terrorism wears on, the U.N. refugee chief said Friday.

"Hundreds of thousands ... are on the roads," Ruud Lubbers, the High Commissioner for Refugees, said at a briefing at the United Nations.

He said that the bombed cities of Jalalabad and Kandahar have emptied out. The U.S. air war against terrorism that began Oct. 7 has targeted both cities. Kandahar is the headquarters of the ruling Taliban militia.

But Lubbers stressed that the large majority of Afghans leaving their homes have fled into the mountains of Afghanistan and have not tried to go to Pakistan.

Pakistan, which has some 2 million Afghan refugees from earlier wars and drought, has officially closed its borders to new arrivals but 60,000 Afghans have crossed into the country over mountain roads since the U.S. bombing began, Lubbers said.

In the past week, he said, about 2,000 a day have been fleeing into Pakistan and "this will go exponentially further."

Lubbers said Pakistan and Iran, which also has also shut its border to Afghan refugees, must relax their stance against new arrivals.

While Pakistan keeps its border shut, the U.N. agency has been caring for new arrivals at temporary sites along the frontier.

He said that Pakistan must "understand that the misery of the people is such that they have to become more forthcoming.

Lubbers said that his agency can handle 5,000 refugees a day if it gets the cooperation, mainly of Pakistan.

He said that the agency's worst case scenario had been 1.5 million new refugees, but it prepared shelters and blankets for 390,000 _ 300,000 in Pakistan and 90,000 in Iran.

"There are now indications that this was not so unrealistic," he said.

He explained that although thousands are fleeing their homes, they are staying within Afghanistan.