SLAMABAD, Pakistan, Sept. 26 ・Thousands of Afghan protesters turned a Taliban march to the abandoned American Embassy in Kabul into a frenzied attack today, chanting Osama bin Laden's name and waving white flags of Islam as they torched the compound, burned American flags and hacked at the mothballed chancery building with an ax.

The embassy, vacated by the last American diplomats in 1989, appeared from television footage to have been largely gutted by the time Taliban officials dispersed the protesters and extinguished the fires. By then, a group of turbaned, black-clad Taliban men had wrenched the seal of the United States off the main embassy building with steel cables and hammers, while others danced ecstatically and shouted "Long live Osama," "Death to America" and "God is great."

The attack followed days of mounting tension across Afghanistan as the militant Muslim clerics of the Taliban rejected American demands to hand over Mr. bin Laden and his associates in the Al Qaeda terrorist organization, and called for a "holy war" against Americans and anybody supporting them if President Bush went ahead with a military attack. With virtually all foreigners now gone from Kabul, the embassy, guarded for more than a decade by Afghan caretakers, made an obvious target.

According to accounts filed to Western news agencies by Afghan reporters who have stayed on in Kabul, the caretakers had fled by the time the protesters, led to the site by a pick-up truck carrying Taliban officials, began storming the embassy gates. The accounts said the demonstrators were mostly Taliban officials and students, but were ambiguous as to whether the razing of the compound was orchestrated or was the result of passions that spiraled spontaneously out of control.

"Some armed men were clearly trying to hold back the crowd and city firefighters worked hard to tackle the blaze, but other Taliban fighters joined in enthusiastically," according to a Reuters account written by Sayed Salahuddin, the news agency's Kabul reporter. He added: "Boys jumped and waved their arms as men used axes to hack at the windows of the main building to gain entry. Amid scenes of pandemonium, fires were started and black smoke billowed into the sky over Kabul."

In Washington, the White House spokesman, Ari Fleischer, said the attack reflected the gravity of the situation 15 days after three hijacked passenger planes were flown into the World Trade Center and the Pentagon. "It's just another sign that this is serious," Mr. Fleischer said. "It doesn't change anything about what the president has said or what the mission of the United States will be."

As the embassy burned, the mission's scope was under discussion 250 miles away, here in the Pakistani capital. Pakistan's military government, despite bitter opposition from powerful Islamic groups within the country, has promised "full support" for any American operation that involves forces flying over, or possibly even staging through, Pakistan.

For a third day, American military officers and representatives of the Central Intelligence Agency met with Pakistani counterparts in Islamabad. No details were released, but a Pakistan Foreign Ministry spokesman, Riaz Mohammed Khan, hinted that any attacks involving Pakistan were still some way off. "No joint operation or contingency plans have been placed before the Pakistan government," he said.

Curiously, the Taliban's supreme leader, Mullah Mohammed Omar, who rejected demands for Mr. bin Laden's handover last week and followed up with a series of bellicose statements accusing the United States of "atrocities" against the Muslim world, chose the moment of the attack on the embassy to issue a new message telling Afghans, vast numbers of them fleeing the major cities as refugees, that the threat of war had diminished and they should return home.

"There is less possibility of an American attack," he said, in a statement issued by the Taliban Information Ministry. "America has no reason, justification or evidence for attacking. Therefore, all those who have been displaced internally or externally are instructed to return to their original place of residence."

A new dimension to the mystery was added on Tuesday when Interpol, the international police agency, issued a bulletin for the arrest of Ayman al-Zawahiri, a 50-year-old Egyptian surgeon who is believed to have been Mr. bin Laden's closest Al Qaeda associate in Afghanistan. The fact that the bulletin was issued two weeks after the attacks could be interpreted as meaning that American officials have concluded that Mr. Zawahiri, at least, has already slipped out of Afghanistan.

Another hint that the United States may now be looking for Al Qaeda leaders elsewhere came from Pakistan, where officials said today that they would not relent in their decision to seal off the country's 1,400- mile border with Afghanistan, a move requested by the Bush administration because, the officials said, they wanted to be sure that none of Mr. bin Laden's men were hiding among the huge tide of refugees.

Another reason Pakistan has given for keeping the borders closed has been that it fears being swamped by up to a million Afghans.