At least 72 people have been killed and 140 left wounded after two suicide bombers and gunmen attacked crowds at Kabul airport in Afghanistan.
At least 60 Afghans and 12 US troops were killed, officials said and US officials said 11 Marines and one Navy medic were among those who died in the attack.
They said another 12 service members were wounded and warned the toll could grow.
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The Ministry of Defence confirmed no British troops or personnel are among the casualties.
One of the bombers struck people standing knee-deep in a wastewater canal under the sweltering sun and those who moments earlier had hoped to get on flights out could be seen carrying the wounded to ambulances in a daze, their own clothes darkened with blood.
A US official said the complex attack was believed to have been carried out by the Islamic State group.
The IS affiliate in Afghanistan is far more radical than the Taliban, who recently took control of the country in a lightning blitz and condemned the attack.
Western officials had warned of a major attack, urging people to leave the airport, but that advice went largely unheeded by Afghans desperate to escape the country in the last few days of an American-led evacuation before the US officially ends its 20-year presence on August 31.
Emergency, an Italian charity that operates hospitals in Afghanistan, said it had received at least 60 patients wounded in the airport attack, in addition to 10 who were dead when they arrived.
Marco Puntin, the charity's manager in Afghanistan said: "Surgeons will be working into the night."
The wounded overflowed the triage zone into the physiotherapy area and more beds were being added, he said.
Pentagon spokesman John Kirby said there were casualties, including among members of the military, but gave no figure. He said one explosion was near an airport entrance and another was a short distance away by a hotel.
Boris Johnson has vowed to continue the evacuation effort in Afghanistan following the "barbaric" attack.
The Prime Minister said the "overwhelming majority" of eligible people have already been helped to flee the Taliban by the RAF and "we are going to keep going up until the last moment" as the deadline rapidly approaches.
No10 said the PM has been "updated on the situation" before chairing a COBRA meeting earlier this evening.
He told reporters in Downing Street that the the evacuation programme would work "flat out" according to "the timetable we've got".
He said: "That's what we're going to do because the overwhelming majority of those who are eligible have now been extracted from Afghanistan."
