Updated 6pm

Last-ditch evacuation flights took off from Kabul airport on Friday, a day after twin suicide bombings on crowds trying to flee Taliban-controlled Afghanistan killed scores of people, including 13 US servicemen and two UK nationals.

According to Al Jazeera’s team in Afghanistan, at least 110 people were killed.

Other media outlets have put the death toll at 170. 

The blasts, claimed by the Islamic State jihadist group, injected further panic into the final days of an already frenzied US-led airlift.

The attacks targeted US forces, but hit hardest the mass of people fearing life under the Taliban who converged on the airport in a desperate bid to board a flight out.

Kabul resident Abdul Majeed said he saw a few hundred people - dead and alive - brought overnight to hospital, as he searched for his younger brother who had been among the crowds.

"My brother was not among them," he told AFP.

US President Joe Biden, under enormous pressure over his administration's handling of the Afghan crisis, vowed to punish those responsible.

"We will not forgive. We will not forget. We will hunt you down and make you pay," he said.

However, determined to end two decades of war in Afghanistan and citing fears of more IS attacks, Biden also insisted that he would stick to his August 31 deadline to end the airlift.

Two UK nationals among dead

Two British nationals and the child of a British national were among the 85 people so-far confirmed killed in the Kabul airport attack, Foreign Secretary Dominic Raab said Friday.

"I was deeply saddened to learn that two British nationals and the child of another British national were killed by yesterday's terror attack, with two more injured," Raab said in a statement.

"These were innocent people and it is a tragedy that as they sought to bring their loved ones to safety in the UK they were murdered by cowardly terrorists."

Refugee exodus

The Taliban have promised a softer brand of rule compared with their first stint in power, which ended in 2001 when the United States invaded following the September 11 attacks.

But many Afghans fear a repeat of their brutal interpretation of Islamic law, as well as violent retribution for working with foreign militaries, Western missions or the previous US-backed government.

On Friday morning, some evacuation flights resumed with queues of people seen lining up on the tarmac but there were no more crowds near the sites of the blasts, according to AFP reporters.

The Taliban had also blocked off the main routes to the airport as well as side roads.

As some Western allies announced an end to their airlifts, many have repeatedly warned that it is impossible to get all at-risk Afghans out by Tuesday. 

About 105,000 people have been flown out of the country since August 14, the day before the Taliban swept to power, according to the White House.

The United Nations said Friday it was bracing for a "worst-case scenario" of up to half a million more refugees from Afghanistan by the end of 2021.

The Taliban has said that Afghans with legal documents will be allowed to travel abroad after the airport reopens to commercial flights.  

'More extreme'

The Taliban have allowed US-led forces to conduct the airlift while they finalise plans for their government to be announced as soon as the American troops have left.

But the Islamic State jihadists, bloody rivals of the Taliban with a record of barbaric attacks, were intent on capitalising on the chaos in Kabul.

In recent years, the Islamic State's Afghanistan-Pakistan chapter has been responsible for some of the deadliest attacks in those countries.

It has massacred civilians at mosques, shrines, public squares and even hospitals.

"These are people that are even more extreme than the Taliban and are basically at war with the Taliban. So it is a horribly complex situation," Australian Defence Minister Peter Dutton said.

Turkish President Recep Tayyip Erdogan said on Friday that Ankara was assessing an offer to run operations at the Kabul airport, with security to be provided by the Taliban. 

Terror, devastation

The blasts hit people trying to reach access gates at the airport, creating scenes of terror and devastation.

Immediately after the first, one man held a semi-conscious victim by the elbow, trying to stop his head from slipping beneath the surface of the fetid water in a canal along the perimeter of the airport.

"I will never, ever want to go (to the airport) again. Death to America, its evacuation and visas," Milad, who was near the first blast with his wife and three children, told AFP.

The Italian NGO Emergency said the hospital it operates in Kabul had been overwhelmed by more than 60 casualties, 16 of whom were pronounced dead on arrival.

The injured "could not speak, many were terrified, their eyes totally lost in emptiness, their gaze blank", the hospital's medical coordinator Alberto Zanin said in a post on the group's Twitter account.

'Bear responsibility'

The attacks led to the worst single-day death toll for the US military in Afghanistan since 2011.

A clearly shaken Biden went before TV cameras to address the American people, describing the killed US troops as heroes.

Asked by a reporter if he bore any responsibility for the deaths, Biden said: "I bear responsibility fundamentally for all that's happened of late." 

The Taliban, which condemned the blasts, emphasised they happened in an area under US military control.