TALIBAN forces appeared to be fleeing Kabul last night as the opposition Northern Alliance said their troops had pushed to the gates of the Afghan capital.

As US jets patrolled the skies, witnesses saw cars, trucks and armoured personnel carriers filled with Taliban soldiers heading towards the Islamic rulers' southern stronghold of Kandahar.

Those remaining in Kabul were becoming increasingly nervous, and a ring of Taliban tanks surrounded the city in anticipation of a full assault from the 6,000 alliance fighters who, in some places, are just four miles away.

Late yesterday, a missile slammed into a Kabul suburb, home to several prominent Taliban officials, as well as Arabs, Chechens and Uzbeks believed to be linked to terrorist suspect Osama bin Laden.

Jubilant opposition fighters near Jabal Saraj, about 45 miles north of Kabul, said Taliban soldiers in several key strongholds on the western side of the contested Shomali plain were surrendering.

The speed of the Taliban's collapse across the northern part of the country suggested large-scale defections to the alliance, with Downing Street claiming the regime was running out of money to pay its supporters.

"The Taliban are fast running out of money. Very large numbers of their troops and functionaries have not been paid for some time. Many are being paid less than a dollar a day and many are defecting," he said.

"There is no doubt that Taliban morale will not be in good shape."

The action north of Kabul came as opposition fighters entered Herat, the main city in western Afghanistan, and were reported to be closing in on the last Taliban stronghold in the north. Iranian radio, broadcasting from Herat, said Taliban troops were fleeing or surrendering.

Tehran radio reported that the opposition forces had also taken control of Kunduz, the last northern city still held by the Taliban.

The alliance's advance started on Friday with the capture of Mazar-e-Sharif. Yesterday in the city, men lined up at barber shops to have their Taliban-mandated beards shaved off. Women were discarding the all-encompassing burqas, and music - banned by the Taliban - could be heard coming from cassette players in shops, according to the Afghan Islamic Press.

The north of Afghanistan is largely made up of ethnic Tajiks, Uzbeks and Shiite Muslims which reflects the mix within the Northern Alliance. However, the alliance has yet to make headway in the south of the country which is populated mostly by ethnic Pashtuns - the same ethnic group as the Taliban. It is unclear whether the alliance can maintain its momentum into the Taliban heartland.

However, the alliance's speedy advance - its control of Afghanistan has risen from ten per cent to 40 per cent in just three days - has given added urgency to the diplomatic efforts to secure a ''broad-based'' government to replace the Taliban.

President George Bush has urged the opposition not to seize the capital until a new government is ready to take over. Britain and America are both anxious to avoid any repeat of the bloodshed and destruction which followed the fall of the Kabul in 1992 to the Northern Alliance, when an estimated 50,000 people were killed.

Northern Alliance foreign minister, Dr Abdullah Abdullah, said the opposition's 6,000 fighters had stopped at the town of Shakar Dara, four miles north of Kabul.

''This is the last stop,'' said Dr Abdullah. "We stopped because we didn't want to advance into Kabul."

However, some alliance commanders see an offensive as inevitable.

"The Taliban will take people inside the city as hostages. It will be our job to defend the people."

l British troops played a "very significant'' part in the rapid advance of the Northern Alliance forces across Northern Afghanistan, Geoff Hoon, Defence Secretary, said yesterday.

The troops, believed to be mainly SAS, have been liaising with the Northern Alliance fighters and advising them how to move forward.

"They've played a very significant part, introducing consistency between the bombing and the movement on the ground," said Mr Hoon