ISLAMABAD -- After almost a week of U.S. military threats against the radical Taliban movement, the only visible result is a fast-rising refugee disaster in Afghanistan and Pakistan.

As many as a million refugees are fleeing from Afghanistan's cities, streaming toward the borders and triggering a new humanitarian catastrophe in a country ravaged by 22 years of war.

Half of the population of two major cities, Kabul and Kandahar, have reportedly abandoned the cities and fled to villages or borders.

While the refugee crisis is surging to unprecedented levels, the mounting pressure of military threats has failed to produce any effect on the Taliban, which controls 95 per cent of Afghanistan.

The Taliban postponed yesterday a council of high-ranking Islamic clerics who were supposed to decide the fate of Osama bin Laden, the suspected mastermind of the devastating terrorist attacks in New York and Washington last week.

The meeting of several hundred clerics from across the country is now scheduled to begin today in Kabul, but there is no assurance of a swift decision on whether to surrender the Saudi millionaire fugitive, who has been sheltered in secret locations in Afghanistan since 1996.

A high-level Pakistani delegation, headed by military intelligence chiefs, returned to Islamabad last night after two days of meetings with Taliban leaders in Kandahar and Kabul.

There was little sign of any real progress in the delegation's efforts to persuade the Taliban to surrender Mr. bin Laden. The Taliban continued to set conditions that were clearly unacceptable to Washington, including a demand for a trial in an Islamic country or before an Islamic judge.

"The delegation conveyed in stark terms the gravity of the situation and what the international community expects from Afghanistan's leadership," Pakistani Foreign Ministry spokesman Riaz Khan said yesterday.

"The purpose of the delegation was not to negotiate, but to impress upon the Taliban leadership the gravity of the situation."

A senior Taliban leader said it would declare a holy war against the United States if there are American military strikes on Afghanistan.

"God is on our side, and if the world's people try to set fire to Afghanistan, God will protect us and help us," Mullah Mohammed Hasan Akhund told Radio Shariat yesterday.

"If America attacks our homes, it is necessary for all Muslims, especially for Afghans, to wage a holy war."

If the call for a holy war is heard, U.S. military attacks could spark a much bigger war.

Already there are escalating numbers of anti-American street protests by Islamic militant groups in Pakistan, including a rally by 5,000 stick-wielding students in Karachi yesterday. Muslim groups have called a general strike for Friday. And tribes in northwestern Pakistan are reportedly mobilizing large groups of young men to join the Taliban to fight against the United States.

One of Pakistan's leading newspapers, The News, reported yesterday that the northern border regions near Afghanistan have been gripped by "religious fervour" and "repeated vows from the mosques that people be ready to raise arms against a foreign army."

The Foreign Ministry's Mr. Khan confirmed that the Pakistani military has been placed on "heightened vigilance" in the northern border regions.

He also confirmed the growing signs of a refugee disaster.

"There are hundreds of thousands of Afghan refugees who we understand are moving toward Pakistan," Mr. Khan told reporters at a briefing. "This is a mass of humanity coming toward Pakistan."

Several thousand refugees have massed at each of the major border crossings between Afghanistan and Pakistan, he said.

Pakistan closed its borders to Afghan refugees on Monday, leaving thousands stranded at the borders to endure hot weather, water shortages and poor sanitation. Some aid workers estimate that a million Afghans are on the move.

The United Nations refugee agency, UNHCR, said it was told by the Pakistani government that about 5,000 Afghans are stranded at a border crossing near the city of Quetta. It said the Taliban is harassing the refugees by setting up new checkpoints on the road from Kabul to the Pakistan border, restricting the number who can reach the border.

Afghans have also been trying to reach their country's border with Tajikistan, Russian officials said yesterday.

Tajikistan is not prepared to take in any, nor is Iran, which has also closed its border with Afghanistan.