U.S. President Joe Biden has vowed to hunt down those responsible for the planned suicide attacks near Kabul airport that have killed 13 U.S. service personnel.

Islamic State Khorasan (ISIS-K), an affiliate of the extremist group in Syria and Iran, claimed responsibility for the attack.

"We will not forgive, we will not forget. We will hunt you down and make you pay," Biden said at the White House, as he confirmed he has asked the Pentagon, responsible for U.S. defense, to draw up plans to retaliate. 

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At least 85 people were killed after two explosions close to the perimeter of Kabul international airport, where thousands had gathered in a desperate attempt to flee Afghanistan after the Taliban seized control.

Wounded men and women in blood-soaked clothes were ferried away from the scene in wheelbarrows, while a boy clutched the arm of a man with a head injury, AFP reported.

Pentagon spokesman John Kirby said one blast occurred near the airport's Abbey Gate and the other close to the nearby Baron Hotel. Two U.S. officials said at least one of the explosions appeared to be from a suicide bombing.

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 organization's Twitter account.

Following the news, China joined a growing number of countries and religious leaders who have condemned the attacks, as China's Foreign Ministry spokesperson Zhao Lijian told reporters, "we hope that relevant parties can take effective measures to ensure a smooth transition of the situation in Afghanistan and ensure the personal safety of the Afghan people." 

UK Prime Minister Boris Johnson described the attacks as "barbaric" and defense secretary Ben Wallace said the country's involvement in the airlift evacuation program will end on Friday lunchtime.

French President Emmanuel Macron sent his "condolences to the families of the American and Afghan victims" and Spanish Prime Minister Pedro Sanchez said "the international community stands with the Afghan people."

The Taliban also condemned the blasts, but noted that they happened in an area under the control of the U.S. military. 

"The Islamic Emirate strongly condemns the bombing targeting civilians at Kabul airport," said a statement on Twitter. "The explosion took place in an area where U.S. forces are responsible for security."

Intelligence warnings

Western countries have been warning of a potential attack by Islamic State militants in the hours before the explosions. ​​In an alert on Wednesday, the U.S. Embassy in Kabul advised citizens to avoid traveling to the airport and said those already at the gates should leave immediately.

The Taliban, whose fighters are guarding the perimeter outside the airport, are enemies of the Afghan affiliate ISIS-K.

The extremist group was formed from the remnants of ISIS and Al Qaeda in the mountainous regions between Afghanistan and Pakistan. Its position is hostile to the West but also to the Taliban, whom ISIS-K believes should have no communication whatsoever with Washington or Europe.

Following the explosions, German officials told Reuters it has completed its evacuation operation. Canada halted evacuations, while Belgium ended operations earlier on Thursday, Prime Minister Alexander De Croo citing the growing threat of a "suicide bomb attack."

ISIS-K is very much a threat to the people in Afghanistan, according to Colin Clarke, the Director of Policy and Research at the Soufan Group.

"This is an affiliate or franchise group spun out of core ISIS in Iraq and Syria – just as bloodthirsty, just as draconian, and just as willing to wantonly kill civilians and slaughter them," he told CGTN Europe.

Red line on August 31

In the past 24 hours evacuation flights have landed in Washington, Mexico, Spain, France, Belgium, Germany, South Korea and Australia.

More than 100,000 Afghans and foreigners have fled Afghanistan via the U.S.-led airlift since the Taliban took control of the country on August 15.

Despite the U.S. and other nations warnings of a looming terror threat, huge crowds of people continued to throng the airport, becoming increasingly anxious ahead of the August 31 deadline set by U.S President Joe Biden to end evacuations and withdraw troops.

Biden and his aides have not budged on the hard deadline – even as some foreign nations warned they would be forced to leave at-risk Afghans behind.

Video editors: Natalia Luz and Nuno Fernandes. Graphics editor: James Sandifer. With contributions from Gary Parkinson and Simon Ormiston