WASHINGTON (REUTERS, NYTIMES) - US President Joe Biden, his voice breaking with emotion, vowed on Thursday (Aug 26) to avenge the Afghan attack, saying the United States would hunt down those responsible for twin explosions at the Kabul airport and that he had asked the Pentagon to develop plans to strike back at them.

Mr Biden spoke hours after the blasts killed at least 85 people, including 13 American troops and scores of civilians, the worst day of casualties for US forces there in a decade.

A health official and a Taleban official said the toll of Afghans killed had risen to 72, including 28 Taleban members, although a Taleban spokesman later denied that any of their fighters guarding the airport perimeter had been killed.

Islamic State Khorasan (ISIS-K), an affiliate of militants who previously battled US forces in Syria and Iraq, claimed responsibility for the attack, saying that one of its suicide bombers targeted "translators and collaborators with the American army".

"To those who carried out this attack, as well as anyone who wishes America harm, know this: We will not forgive," Mr Biden said in remarks at the White House, using language that had grim echoes of warnings President George W. Bush made after the terror attacks on Sept 11, 2001. "We will not forget. We will hunt you down and make you pay."

He added: "I have also ordered my commanders to develop operational plans to strike ISIS-K assets, leadership and facilities. We will respond with force and precision at our time, at the place we choose and the moment of our choosing."

Mr Biden promised US evacuations would continue.

"We will not be deterred by terrorists, we will not let them stop our mission. We will continue the evacuations," he said.

White House spokeswoman Jen Psaki told reporters that Mr Biden was sticking to his Tuesday pull-out target for withdrawing US forces, saying he was doing so on the advice of military advisers concerned about more attacks.

She said Mr Biden was working to get out every American who wanted out by the deadline. "Our commitment to them does not end," she said.

Vice-President Kamala Harris cancelled her plan to campaign for California Democratic Governor Gavin Newsom, who is facing a recall election on Sept 14, on her way home from a trip to Asia, and will instead return to Washington, her staff said.

General Frank McKenzie, head of US Central Command, said US commanders were on alert for more attacks by Islamic State, including possibly rockets or vehicle-borne bombs targeting the airport.

"We're doing everything we can to be prepared," he said.

Biden's biggest fear

Thursday's attack was exactly what Mr Biden had feared the most: His decision to end America's longest war was driven, he had said repeatedly, by his determination not to sacrifice even one more member of the military on behalf of an effort he had long believed was no longer in the interests of the US.

But the withdrawal he set in motion claimed the lives of 13 US troops, along with at least 72 Afghan civilians and counting - the first American casualties in Afghanistan in 18 months and the deadliest day there for the US military since 2011.

Mr Biden appeared to be fighting back tears and his voice cracked with emotion as he expressed "heartache" over the American "heroes" who died. "It's been a tough day," he said.

The President hailed the sacrifice of the soldiers, 12 of whom were Marines, who lost their lives, and the 18 other American service members who were injured in the blasts.

He pledged that the US would uphold its "sacred obligation" to the families of the fallen in Afghanistan, calling those who died in the attacks "heroes who have been engaged in a dangerous, selfless mission to save the lives of others".

He added he had told the US military that he would grant additional force if they needed it: "Whatever they need, if they need additional force, I will grant it."

Mr Biden said that as president, he bore responsibility "for all that's happened", but he again denied that his decision to withdraw forces by the end of the summer led inevitably to the chaotic scenes of evacuation at the airport, or to the deaths at the hands of the terrorists.

The President defended his handling of his most serious foreign policy crisis, saying ultimately it is his responsibility, while assigning some blame to his predecessor, Republican Donald Trump, for the 2020 agreement Mr Trump negotiated with the Taleban.

"I had only one alternative: for thousands of more troops back into Afghanistan," Mr Biden said. "I have never been of the view that we should be sacrificing American lives to try to establish a democratic government in Afghanistan."

Caught off-guard

Acting against the advice of his generals and overruling some of his top foreign policy advisers, Mr Biden had in April announced his decision to withdraw the remaining 2,500 US troops from the country. He has said that he did not want to call the parents of another Marine, soldier or airman killed in action in Afghanistan.

But the rapid takeover of the country by the Taleban caught the administration off-guard and set in motion a chaotic evacuation in which almost 6,000 American troops tried to secure the Kabul airport against the Taleban and terror groups. Earlier this week, Mr Biden rejected calls from lawmakers, activists and other world leaders to extend the American presence at the airport past Aug 31, citing the potential for terrorist attacks.

He said he did not trust the Taleban but believed that - for now - the Taleban appeared to be interested in cooperating with the US and other Western nations, and that it was in their interests to do so.

Since Aug 14, just before the Taleban seized control of Kabul, the administration says it has evacuated more than 100,000 people, ferrying them to safety. But the administration concedes that there are still more Americans and Afghan allies who want to leave the country.

Ms Psaki said the US also had "an enormous amount of leverage" - including economic leverage - over the Taleban, which is subject to US and UN sanctions.

The Afghan government has also long relied on transfers of dollars from their central bank assets, many of which are held in the US. An administration official said any such assets would not be made available to the Taleban.

A Taleban spokesman described the attack as the work of "evil circles" who would be suppressed once foreign troops leave.

A Taleban official lamented the number of his members killed, saying they had lost more men that the Americans, but Taleban spokesman Zabihullah Mujahid later said no Taleban were killed in the twin blasts.

"That part of the airport is under the direct control of U.S. forces so we weren't there," he said.

While Western countries fear that the Taleban, who once sheltered Osama bin Laden's al Qaeda, will allow Afghanistan to turn again into a haven for militants, the militant group says they will not let the country be used by terrorists.

ISIS-K was initially confined to areas on the border with Pakistan but has established a second front in the north of the country. The Combating Terrorism Centre at West Point says ISIS-K includes Pakistanis from other militant groups and Uzbek extremists in addition to Afghans.

A Taleban official said at least 28 members of the militant group were killed in the attack.

"We have lost more people than the Americans in the airport blast," he said, adding that the Taleban was "not responsible for the chaotic evacuation plan prepared by foreign nations".

A US Central Command spokesman said 18 US soldiers injured in the attack were "in the process of being aeromedically evacuated from Afghanistan on specially equipped C-17s with embarked surgical units".

In his speech on Thursday, Mr Biden asked for a moment of silence to remember those who died.

"Each one of these women and men of our armed forces are the heirs of that tradition," he said, "of sacrifice, of volunteering to go into harm's way, to risk everything, not for glory, not for profit, but to defend what we love and the people that we love."

Carnage

Pentagon officials described the bombing at the airport as a "complex attack" that included at least two explosions and gunfire by ISIS-K fighters at Americans and civilians.

Gruesome videos of dead bodies outside the walls around the airport were circulated widely online. Videos shot by Afghan journalists showed dozens of corpses strewn around a canal by the airport fence. Some were being fished out and laid in heaps as wailing civilians searched for loved ones.

"For a moment I thought my eardrums were blasted and I lost my sense of hearing. I saw bodies and body parts flying in the air like a tornado blowing plastic bags. I saw bodies, body parts elders and injured men, women and children scattered," said one Afghan who had been trying to reach the airport.

"That little water flowing in the sewage canal had turned into blood."

Mr Zubair, a 24 year-old civil engineer, who had been trying for a nearly week to get inside the airport with a cousin who had papers authorising him to travel to the US, said he was just 50m from a suicide bomber who detonated explosives at the gate.

"Men, women and children were screaming. I saw many injured people - men, women and children - being loaded into private vehicles and taken toward the hospitals," he said, adding that after the explosions there was gunfire.

Global condemnation

World leaders on Friday condemned the "despicable" attack.

Britain's Prime Minister Boris Johnson denounced the attack as "barbaric", paying tribute to the "phenomenal effort" of those involved in the evacuation operation. He added that Britain would "keep going up until the last moment".

France's President Emmanuel Macron also pledged to see the evacuations "through to the end", as he offered "his condolences to the families of the American and Afghan victims" and saluted "the heroism of those who are on the ground to carry out the evacuation operations".

Saudi Arabia's Foreign Ministry rejected the attacks as "incompatible with all religious principles and moral and human values" and said that it stood "with the Afghan people".

Prior to the attack, several nations had announced earlier in the day that they were halting their evacuations from the Kabul airport as governments around the world gave dire warnings about threats to the crowds gathered there in an attempt to flee Afghanistan.

A NATO country diplomat in Kabul said all foreign forces were aiming to evacuate their citizens and embassy employees by Aug 30.

The Taleban would tighten security around the airport, said the diplomat who declined to be identified.

"Security is their responsibility," the diplomat said, adding that the Taleban should investigate the Islamic State network.