Islamic State suicide bombers attacked crowds of people gathered Thursday outside Kabul airport hoping to flee Taliban-controlled Afghanistan, killing dozens including 13 US troops, as President Joe Biden vowed to hunt down those responsible.

The Taliban said the two blasts killed between 13 and 20 people. A health official in the previous government said the toll could rise to 60.

The Islamic State group claimed responsibility for the attack, which added more urgency and heartbreak to the frantic US-led campaign to airlift people out of Afghanistan now that the hardline Islamist group has seized power.

Kabul international airport
Map locating the international airport in Kabul. Photo: AFP / Valentina BRESCHI

The airport blasts came as the August 31 deadline looms for the United States to withdraw its troops, and for it and other Western countries to end a massive airlift that has already evacuated nearly 100,000 people.

With the crisis in Afghanistan rocking his presidency to the core, a clearly shaken Biden went before TV cameras to address the American people after the worst single-day death toll for the US military in Afghanistan since 2011.

He said the US soldiers who died in the airport blasts were heroes, and vowed to catch those behind the attack. "We will not forgive. We will not forget. We will hunt you down and make you pay," he said.

Afghanistan evacuation
Nearly 90,000 people have fled Afghanistan since the Taliban took control Photo: US AIR FORCE / Donald R. ALLEN

Biden said the evacuation effort would proceed and end on schedule at the end of the month.

Asked by a reporter if he bore any responsibility for the death of the US service members killed Thursday, Biden said: "I bear responsibility fundamentally for all that's happened of late."

The attack marked a deadly escalation of the drama unfolding at the airport. It is the only part of the country under foreign control following the Taliban's return to power on August 15, and huge crowds have massed in the hope of being evacuated.

Kabul airport
IMAGES Wide shot images of planes taking off from Kabul Airport on Wednesday. More than 80,000 people have been evacuated since August 14, many are still hoping to flee the threat of reprisals and repression in Taliban-ruled Afghanistan. Photo: AFPTV

Taliban spokesman Zabihullah Mujahid told AFP that between 13 and 20 people were killed and 52 wounded in the twin blasts, while Kabul hospitals reported six dead and up to 90 wounded.

A health official in the pre-Taliban administration said the death toll could rise to 60, but added that he could not be named and other sources could not confirm the figure.

General Kenneth McKenzie, head of the US Central Command, initially said 12 US troops were killed. But another soldier died later, and the latest US injury toll is 18, the Central Command said.

Kabul airport
A satellite image by Maxar Technologies shows crowds of people waiting on the tarmac at Kabul’s Hamid Karzai International Airport in Afghanistan Photo: Satellite image ©2021 Maxar Technologies / -

McKenzie said an unspecified number of Afghan civilians were killed.

McKenzie said the blasts have been assessed as coming from Islamic State suicide bombers, and that the US airlift would continue despite the attack.

"ISIS will not deter us from accomplishing the mission," he said.

The United States expects more Islamic State attacks in Kabul and is prepared to retaliate, McKenzie told a news conference.

Later, in the early hours of Friday, a huge blast was heard in Kabul. Mujahid said this was a controlled explosion by US troops destroying equipment at the airport, a statement that has yet to be independently confirmed.

Biden had earlier cited an "acute" terrorist threat from the regional chapter of the jihadist group.

Afghanistan evacuations
Over 80,000 people have been evacuated since August 14, but huge crowds remain outside Kabul airport hoping to flee the threat of reprisals and repression in Taliban-led Afghanistan. Photo: US AIR FORCE / Donald R. ALLEN

The Taliban, a rival of the Islamic State, condemned the blasts, and said they happened in an area under US military control.

Graphic video shared on social media showed bodies lying semi-submerged in a canal adjacent to the airport, where thousands have gathered since the Taliban takeover of August 15 hoping for a flight out.

Afghanistan
Afghans board a U.S. Air Force C-17 Globemaster III for evacuation at Hamid Karzai International Airport Photo: US AIR FORCE / Donald R. ALLEN

"When people heard the (first) explosion there was total panic," a man name Milad told AFP.

"The Taliban then started firing in the air to disperse the crowd. I saw a man rushing with an injured baby in his hands."

The US government and its allies had raised the alarm earlier in the day with a series of advisories warning their citizens to avoid the airport.

After the blasts, images posted on social media showed men ferrying wounded people to safety in wheelbarrows.

In another picture, a boy was seen clutching the arm of a man whose clothes were soaked in blood.

More than 95,000 Afghans and foreigners have fled Afghanistan via the US-led airlift since the hardline Taliban movement took control of the country.

Biden has not budged on the August 31 deadline -- even as some foreign nations warned they would be forced to leave at-risk Afghans behind.

Several Western allies have already wrapped up their airlift operations including Canada, whose government said it was "truly heartbreaking" to leave behind those who wanted to be rescued.

The airport attack on unarmed people desperate to flee to safety drew condemnation from around the world, with Britain describing it as barbaric and Germany as heinous. The United Nations called an urgent meeting of the permanent members of the Security Council for Monday.

In Washington, Republicans said Congress should end its summer vacation and reconvene to discuss what they called the chaotic US withdrawal from Afghanistan.

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.

The group has especially targeted Muslims from sects it considers heretical, including Shiites.

But while IS and the Taliban are both hardline Sunni Islamist militants, they are rivals and oppose each other.

The Taliban have promised a softer brand of rule from their first stint in power, which ended in 2001 when the United States invaded because they gave sanctuary to Al-Qaeda.

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

There are particular concerns for women, who were largely banned from education and employment and could only leave the house with a male chaperone during the group's 1996-2001 rule.

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