US President Joe Biden ordered American military commanders to develop operational plans to strike ISIS-Khorasan assets, leadership and facilities as the death toll of suicide blasts at Kabul airport rose to 85.

Two blasts and gunfire rocked the area outside the airport on Thursday evening, witnesses said. Videos shot by Afghan journalists showed dozens of bodies strewn around a canal on the edge of the airport.

A health official and a Taliban official said the toll of Afghans killed had risen to 72, including 28 Taliban members. The US military said 13 of its service members were killed.

ISIS-Khorasan, an Islamic State affiliate claimed responsibility. ISIS, an enemy of the Taliban as well as the West, said one of its suicide bombers targeted "translators and collaborators with the American army".

US officials also blamed the group and vowed retribution.

"To those who carried out this attack, as well as anyone who wishes America harm, know this: We will not forgive. We will not forget. We will hunt you down and make you pay," said Biden while addressing his nation from the White House soon after the attack.

“We will respond with force and precision, at our time, at the place we choose and at the moment of our choosing,” he said.

“I will defend our interests and our people with every measure at my command."

Biden also indicated that he could send more military assistance to Afghanistan if he felt the need for it. "I've instructed the military (to act) with whatever they need. If they need additional force, I will grant it,” he said.

The attacks, he said, had only increased the determination of the US military to carry on its mission.

Biden said that the service members who lost their lives in Kabul on Thursday were "heroes" and "the best the country has to offer".

"The lives we lost today were lives given in the service of liberty, the service of security, the service of others, in the service of America," he said.

He also defended relying on the Taliban to provide security outside the Kabul airport.

"We are counting on them to act in their own self-interest," he said. "And it's in their interest that we leave when we said we would. There is no evidence thus far from our commanders in the field that there has been collusion between Taliban and ISIS."

Biden’s chief diplomat — US State Secretary Antony Blinken — used the attacks to argue that the president’s decision to withdraw US forces from Afghanistan was right.

“The bombings around the Kabul airport were a devastating reminder of the dangerous conditions in which our service members and diplomats are operating as we conclude the United States’ 20-year military mission in Afghanistan," he said.

US Defence Secretary Lloyd J. Austin reminded Americans that the terrorists took the lives of American service members “at the very moment they were trying to save the lives” of others.

“We mourn their loss. We will treat their wounds. And we will support their families […] but we will not be dissuaded from the task at hand,” the US defence chief declared.

US on alert for more attacks

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

"We're doing everything we can to be prepared," he said, adding that some intelligence was being shared with the Taliban and that he believed "some attacks have been thwarted by them."

A video taken in the aftermath of the attack of the attack showed corpses in a wastewater canal by the airport fence, some being fished out and laid in heaps while wailing civilians searched for loved ones.

"I saw bodies and body parts flying in the air like a tornado blowing plastic bags," said one Afghan witness. "That little water flowing in the sewage canal had turned into blood."

Zubair, a 24-year-old civil engineer, said he was close to a suicide bomber who detonated explosives.

"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.

'Chaotic evacuation'

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

A Taliban official lamented the number of Taliban members killed in the ISIS attack.

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

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

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

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

Western countries fear that the Taliban, who once sheltered Osama bin Laden's Al Qaeda, will allow Afghanistan to turn again into a haven for militants. The Taliban say they will not let the country be used by terrorists.

Airlift continues

The United States would press on with evacuations despite the threat of further attacks, McKenzie said, noting that there were still about 1,000 US citizens in Afghanistan.

The pace of evacuation flights had accelerated on Friday and American passport holders had been allowed to enter the airport compound, said a Western security official stationed inside the airport.

In the past 12 days, Western countries have evacuated nearly 100,000 people. But they acknowledge that thousands will be left behind when the last US troops leave at the end of the month.

Several Western countries said the mass airlift of civilians was coming to an end and announced their last remaining troops had left the country.

The American casualties in Thursday's attack were believed to be the most US troops killed in Afghanistan in a single incident since 30 personnel died when a helicopter was shot down in 2011.

The US deaths were the first in action in Afghanistan in 18 months, a fact likely to be cited by critics who accuse Biden of recklessly abandoning a stable and hard-won status quo by ordering an abrupt pullout.