International flights to Afghanistan were banned and overseas assets of its radical Islamic rulers were frozen today when the Taliban regime refused to comply with a U.N. demand to turn over fugitive Saudi businessman Osama bin Laden to face prosecution in the United States for terrorism.

Taliban officials asked the United Nations Saturday to postpone the sanctions, which the Security Council approved a month ago, and called for talks with the United States. But they continued to assert that bin Laden is an honored guest and cannot be handed over to "infidels." U.S. authorities suspect the Saudi millionaire, a sworn enemy of the West who has lived in Afghanistan since 1996, of financing and orchestrating the August 1998 bombings of two U.S. embassies in East Africa in which 224 people died.

As the United Nations had prepared to implement the sanctions at the behest of U.S. officials, authorities in Pakistan continued to investigate Friday's rocket attacks in Islamabad aimed at the U.S. Embassy and other American and international buildings. Pakistani authorities said they had not identified any suspects.

But U.S. officials and Pakistani experts said the attacks, which injured six people, could be a warning to the international community not to pressure Afghanistan or bin Laden, who is a hero to many Islamic fundamentalists. The Taliban is an Islamic militia that controls 90 percent of Afghan territory.

In Washington, the State Department issued a "worldwide caution" to all Americans abroad, urging them not to travel to Afghanistan and to be alert to any action by the Taliban..

At least a half-dozen radical Islamic groups in Pakistan, many with ties to the Taliban, have warned publicly that they would avenge any foreign move against Afghanistan or bin Laden. One Islamic cleric asserted last month that his followers would target Americans if the United States attacked Afghanistan.

"Osama is not just a name, he is a phenomenon that embodies the jihads [holy wars] being fought from Central Asia to Kashmir," a spokesman for one Pakistani Islamic group said last month. Bin Laden, an heir to a Saudi construction fortune, is alleged to have financed numerous foreign attacks by Islamic terrorists. He has denied being behind the attacks, and his whereabouts in Afghanistan are not known.

The Taliban's top leader, Mohammad Omar, condemned the Islamabad bombings on Friday, suggesting they were part of a plot to undermine his government's ties with Pakistan and the West. But before the attack, other Taliban officials had warned that the United States would face divine retribution, including "storms and earthquakes," if it tried to harm bin Laden.

"We will never hand over Osama bin Laden, and we will not force him out," the Taliban's foreign minister, Wakil Ahmad Muttawakil, said Tuesday. "He will remain free in defiance of America. . . . We will not hand him to an infidel nation."

On Wednesday, about 50,000 Afghans demonstrated in Kandahar, the city that serves as the Taliban's headquarters, protesting the impending sanctions by throwing stones at U.N. buildings and burning U.S. flags. According to one report, an Islamic guerrilla group called al Qaida warned that a special commando unit had been formed to take revenge if the sanctions were imposed.

"By keeping Osama, the Taliban are sending a loud message to the world that their land cannot be touched," said Massood Kalili, an Afghan diplomat in New Delhi who represents the government deposed by the Taliban. "They fear that if the United States gets him, they will make more demands" on issues such as human rights and drug trafficking.

Earlier this year, the Clinton administration banned all U.S. trade and investment in Afghanistan because of the Taliban's refusal to turn over bin Laden. On Oct. 15, the U.N. Security Council followed suit, giving the government one month to give up bin Laden or face more sanctions. The U.N. resolution permits flights to and from Afghanistan for humanitarian and religious purposes.

Some international aid groups have said that the impending sanctions could seriously damage the country's already devastated economy and end all domestic flights by the Afghan national airline, Ariana Afghan Airlines. The airline ferries supplies within Afghanistan, where roads are badly damaged after years of civil war.

Taliban officials have characterized the impending sanctions as a cruel punishment against the Afghan people. Food prices have risen sharply in recent weeks, and tens of thousands of refugees have overwhelmed the capital, Kabul, after fleeing fighting in northern Afghanistan between Taliban forces and an insurgent militia.

Taliban authorities have said they are willing to negotiate with the United States over bin Laden's fate and would even put him on trial if the United States provided evidence that he was involved in terrorism. They also offered to have him judged or monitored by regional Muslim governments. Washington has repeatedly rejected Taliban offers for talks or alternatives to surrendering bin Laden.

Some observers have criticized the United States for being obsessed with bin Laden rather than developing a regional strategy to build allies and contain the spread of Islamic terrorism. Ahmed Rashid, a Pakistani writing in the current issue of Foreign Affairs, said that Washington's "single-minded obsession" with bin Laden is an inadequate policy for dealing with the "increasingly volatile" region.

Whether or not the attacks in Islamabad prove to be linked to the sanctions, the incident has highlighted the difficult choice facing Pakistan's month-old military government over its policy toward Afghanistan.

Pakistan has been one of the Taliban's few international allies, and the Kabul regime has provided fighters for Pakistan's guerrilla war with India over the disputed Himalayan region of Kashmir.

But Pakistan's new ruler, Gen. Pervez Musharraf, wants to promote friendly relations with the United States, and his country badly needs Western aid and loans. Musharraf has said that he will not tolerate Islamic terrorism in Pakistan and that he supports a "truly representative" government in Afghanistan.