US service personnel and Afghans have been killed in several explosions near Kabul airport.
The two blasts occurred at the Abbey Gate and near the Baron Hotel, as western forces continue their evacuation missions from Afghanistan.
A US general said 12 US service members have been killed and 15 more have been injured.
Marine Corps General Kenneth McKenzie, commander of US Central Command, told a news conference: "At this time we know that 12 US service members have been killed in the attack, and 15 more service members have been injured.
"A number of Afghan civilians were also killed and injured in the attack."
The Ministry of Defence (MOD) has said there are no reported UK military or UK Government casualties.
About 1,000 British personnel plus RAF aircraft have been deployed to Kabul's Hamid Karzai International Airport for the evacuation mission, airlifting UK nationals and former Afghan staff out of the country.
US Pentagon Press Secretary John Kirby said the US military and Afghan deaths occurred in a "complex attack" around Kabul's airport, adding: "A number of others are being treated for wounds."
Emergency, a charity that runs war hospitals and first-aid posts across Afghanistan, said about 60 people had been wounded in the blasts and are being treated at a nearby surgical centre.
Boris Johnson said the UK's evacuation mission, named Operation Pitting, will continue despite the "barbaric" events at Kabul airport, with the Prime Minister chairing a COBRA meeting following the events.
NATO Secretary General Jens Stoltenberg, meanwhile, said he strongly condemned the "horrific terrorist attack".
The explosions came following warnings that a terror attack could be launched in the final phase of the evacuation.
James Heappey, the UK's Armed Forces Minister, this morning warned of an "imminent and lethal" threat of an ISIS attack targeting Kabul airport.
He had urged people queuing outside Hamid Karzai International Airport to move to safety amid concerns over an affiliate of the so-called Islamic State (IS) in Afghanistan, known as ISIS-K.
The MOD did not confirm or deny whether ISIS-K was believed to be behind the explosions.
Watch: The ISIS-K group had earlier been identified as a threat to Kabul airport - but who are they?
A UK Government spokesperson said earlier: "We are working urgently to establish what has happened and its impact on the ongoing evacuation effort.
"Our primary concern remains the safety of our personnel, British citizens and the citizens of Afghanistan.
"We are in close contact with our US and other NATO allies at an operational level on the immediate response to this incident."
John Kirby confirmed the first blast, near the Abbey Gate of Kabul's airport, had "resulted in a number of US & civilian casualties".
He tweeted again to confirm "at least one other explosion at or near the Baron Hotel, a short distance from Abbey Gate".
Conservative MP Alicia Kearns, a member of the foreign affairs and national security strategy committees, said there had been "many hurt" in an attack at the Baron Hotel – where Britons and Afghans eligible for repatriation were being processed.
"A bomb or attack with gunfire at northern gate of Baron's Hotel," she said.
"Worried this will devastate evacuation – so many hurt."
Labour leader Sir Keir Starmer described the Kabul airport attack as "devastating".
Writing on Twitter, he said: "Our thoughts are with all those killed and wounded, serving personnel supporting the evacuations and all those desperately trying to leave.
"The bravery of the troops at the airport will always outweigh the cowardice of those who wish to harm us."