(Reuters) -Islamic State struck the crowded gates of Kabul airport in a suicide bomb attack on Thursday, killing scores of civilians and 12 U.S. troops, and throwing into mayhem the airlift of tens of thousands of afghans desperate to flee.

The U.S. death toll, announced General Frank McKenzie, head of U.S. Central Command, made it the deadliest single incident for American forces in Afghanistan in a decade and one of the deadliest of the entire 20-year war.

Afghan health officials were quoted as saying 60 civilians died, but it was not clear whether that was a complete count. Video uploaded by Afghan journalists showed dozens of bodies and wounded victims strewn around a canal on the edge of the airport. At least two blasts rocked the area, witnesses said.

Islamic State, which has emerged in Afghanistan as enemies both of the West and the Taliban, claimed responsibility in a statement in which it said one of its suicide bombers targeted “translators and collaborators with the American army”. U.S. officials also blamed the group.

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

A ditch by the airport fence was filled with blood soaked corpses, some being fished out and laid in heaps on the canal side while 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 in the blast site,” said one Afghan who had been trying to reach the airport

“Bodies and injured were lying on the road and the sewage canal. That little water flowing in the sewage canal had turned into blood.”

McKenzie said the United States would press on with evacuations, noting that there were still around 1,000 U.S. citizens in Afghanistan. But several Western countries said the mass airlift of Afghan civilians was coming to an end, likely to leave no way out for tens of thousands of Afghans who worked for the West through two decades of war.

Violence by Islamic State is a challenge for the Taliban, who have promised Afghans they will bring peace to the country they swiftly conquered. A Taliban spokesman described the attack as the work of “evil circles” who would be suppressed once the foreign troops leave.

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.

SCREAMING

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 authorizing him to travel to the United States, said he was 50 meters from the first of two suicide bombers 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. After the explosions there was gunfire.

Washington and its allies had been urging civilians to stay away from the airport on Thursday, citing the threat of an Islamic State suicide attack.

In the past 12 days, Western countries have evacuated nearly 100,000 people, mostly Afghans who helped them. But they acknowledge that many thousands will be left behind following Biden’s order to pull out all troops by Aug 31.

The last few days of the airlift will mostly be used to withdraw the remaining troops. Canada and some European countries have already announced the end of their airlifts, while publicly lamenting Biden’s abrupt pullout.

AIRPORT DOORS ‘CLOSED’

“We wish we could have stayed longer and rescued everyone,” the acting chief of Canada’s defense staff, General Wayne Eyre, told reporters.

Biden ordered all troops out of Afghanistan by the end of the month to comply with a withdrawal agreement with the Taliban negotiated by his predecessor Donald Trump. He spurned calls this week from European allies for more time.

The abrupt collapse of the Western-backed government in Afghanistan caught U.S. officials by surprise and risks reversing gains, especially in the rights of women and girls, millions of whom have been going to school and work, once forbidden under the Taliban.

Biden has defended the decision to leave, saying U.S. forces could not stay indefinitely. But his critics say the U.S. force, which once numbered more than 100,000, had been reduced in recent years to just a few thousand troops, no longer involved in fighting on the ground and mainly confined to an air base. It was a fraction of the size of U.S. military contingents that have stayed in places such as Korea for decades.

Fighters claiming allegiance to Islamic State began appearing in eastern Afghanistan at the end of 2014 and have established a reputation for extreme brutality. They have claimed responsibility for suicide attacks on civilians, government targets and ethnic and sectarian minorities.

Since the day before the Taliban swept into Kabul, the United States and its allies have mounted one of the biggest air evacuations in history, bringing out about 95,700 people, including 13,400 on Wednesday, the White House said on Thursday.

The Taliban have encouraged Afghans to stay, while saying those with permission to leave will still be allowed to do so once foreign troops leave and commercial flights resume.

The Taliban’s 1996-2001 rule was marked by public executions and the curtailment of basic freedoms. The group was overthrown two decades ago by U.S.-led forces for hosting the al Qaeda militants who masterminded the Sept. 11, 2001 attacks on the United States.

The Taliban have said they will respect human rights in line with Islamic law and will not allow terrorists to operate from the country.

(Reporting by Reuters bureaus; Writing by Stephen Coates, Robert Birsel, Nick Macfie, Peter Graff; Editing by Clarence Fernandez, Simon Cameron-Moore, Frances Kerry, Edmund Blair and Daniel Wallis)