An explosion outside Kabul airport killed at least 60 people, including children, and wounded many Taliban guards, a Taliban official told Reuters.
Earlier, the United States military confirmed that a large explosion occurred outside the airport, as the US-led airlift of thousands continued inside the compound.
“We can confirm an explosion outside Kabul airport. Casualties are unclear at this time. We will provide additional details when we can,” said Pentagon Spokesman John Kirby.
The explosion appeared to be caused by a suicide bomb, US officials said, citing an initial report and cautioning that it could change.
Unconfirmed reports put the explosion at the airport's main Abbey Gate, where thousands of people have massed over the past 12 days hoping to be evacuated after the Taliban seized power.
Other reports located it close to the Baron Hotel near the gate, which Western nations had used to stage some evacuations.
US and allied officials have said they had intelligence that suicide bombers were threatening to attack the airport.
US President Joe Biden has been briefed on the explosion, according to a White House official.
Biden was in a meeting with security officials about the situation in Afghanistan, where the United States is in the final steps of ending its 20-year war, when the explosion was first reported, according to a person familiar with the matter.
Britain's defence ministry said it was working urgently to establish what had happened at Kabul airport following reports of an explosion.
“We are working urgently to establish what has happened in Kabul and its impact on the ongoing evacuation effort,” the defence ministry said on Twitter.
“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.”
However, The Turkish Defence Ministry said there were two explosions, adding that there was no damage to Turkish units.
Earlier today, Western nations warned their citizens to immediately leave the surrounds of Kabul airport over a terrorist threat, as thousands of people try to reach a dwindling number of evacuation flights.
The US government and its allies raised the alarm with a series of coordinated and specific advisories for their citizens to avoid the airport.
“Those at the Abbey Gate, East Gate, or North Gate now should leave immediately,” said the US State Department, citing unspecified “security threats”.
Australia's department of foreign affairs said there was an “ongoing and very high threat of terrorist attack”. “Do not travel to Kabul Hamid Karzai International Airport. If you're in the area of the airport, move to a safe location and await further advice.”
London issued a similar warning, adding “if you can leave Afghanistan safely by other means, you should do so immediately”.