KABUL:The Afghan Taliban tightened their territorial stranglehold around Kabul on Saturday, as refugees from the insurgents' relentless offensive flooded the capital and US Marines returned to oversee emergency evacuations.With the country's second- and third-largest cities having fallen into Taliban hands, Kabul has effectively become the besieged, last stand for government forces who have offered little or no resistance elsewhere.

Insurgent fighters are now camped just 50 kilometres away, leaving the United States and other countries scrambling to airlift their nationals out of Kabul ahead of a feared all-out assault.US embassy staff were ordered to begin shredding and burning sensitive material, as units from a planned re-deployment of 3,000 American troops started arriving to secure the airport and oversee the evacuations.A host of European countries -- including Britain, Germany, Denmark and Spain -- all announced the withdrawal of personnel from their respective embassies on Friday.

For Kabul residents and the tens of thousands who have sought refuge there in recent weeks, the overwhelming mood was one of confusion and fear of what lies ahead.We don't know what is going on," one resident, Khairddin Logari, told AFP.

UN Secretary-General Antonio Guterres said he was "deeply disturbed" by accounts of poor treatment of women in areas seized by the Taliban, who imposed an ultra-austere brand of Islam on Afghanistan during their 1996-2001 rule.

"It is particularly horrifying and heartbreaking to see reports of the hard-won rights of Afghan girls and women being ripped away," Guterres said.The scale and speed of the Taliban advance has shocked Afghans and the US-led alliance that poured billions into the country after toppling the Taliban in the wake of the September 11 attacks nearly 20 years ago.

Days before a final US withdrawal ordered by President Joe Biden, individual soldiers, units and even whole divisions have surrendered -- handing the insurgents even more vehicles and military hardware to fuel their lightning advance.Despite the frantic evacuation efforts, the Biden administration continues to insist that a complete Taliban takeover is not inevitable.

"Kabul is not right now in an imminent threat environment," Pentagon spokesman John Kirby said Friday, while acknowledging that Taliban fighters were "trying to isolate" the city.The Taliban offensive has accelerated in recent days, with the capture of Herat in the north and, just hours later, the seizure of Kandahar -- the group's spiritual heartland in the south.

Kandahar resident Abdul Nafi told AFP the city was calm after government forces abandoned it for the sanctuary of military facilities outside, where they were negotiating terms of surrender."I came out this morning, I saw Taliban white flags in most squares of the city," he said. "I thought it might be the first day of Eid."Pro-Taliban social media accounts have boasted of the vast spoils of war captured by the insurgents -- posting photos of armoured vehicles, heavy weapons, and even a drone seized by their fighters at abandoned military bases.

In Herat, the Taliban captured long-time strongman Ismail Khan, who helped lead the defence of the provincial capital along with his militia fighters.Pul-e-Alam, capital of Loghar province, was the latest city to fall on Friday, putting the Taliban within striking distance of Kabul.Helicopters flitted back and forth between Kabul's airport and the sprawling US diplomatic compound in the heavily fortified Green Zone -- 46 years after choppers evacuated Americans from Saigon, signalling the end of the Vietnam War.

The US-led evacuation is focused on thousands of people, including embassy employees, and Afghans and their families who fear retribution for working as interpreters or in other support roles for the United States.

Pentagon spokesman Kirby said that most of the troops shepherding the evacuation would be in place by Sunday and "will be able to move thousands per day" out of Afghanistan."Capacity is not going to be a problem," he said.