At least 13 civilians, including children, are believed to have been killed in explosions at Kabul Airport in Afghanistan.
Two separate bomb blasts are reported to have happened, with at least one caused by a suicide bomber.
US defence spokesman John Kirby confirmed the blast occurred on Thursday afternoon.
Mr Kirby said: "We can confirm an explosion outside Kabul airport. Casualties are unclear at this time. We will provide additional details when we can."
READ MORE: What people in Liverpool can do to help Afghan refugees
Three US soldiers and Taliban guards are said to have also been injured in the attack.
It was not immediately known if British troops are among the casualties and evacuation planes continued to fly out of Kabul within minutes of the explosion
Seconds after the blast gunmen are believed to have opened fire as the airport came under attack from Islamic State fighters desperate to deal a final blow to the mission.
The “complex attack” came within hours of two suspected Islamic State fighters being seized by Taliban.
It is thought they were caught as they probed the airport for gaps in security.
The attack took place in the canal where people are waiting to see if they can get a flight out of the country, as the deadline for evacuations draws near.
The explosion took place close to the American area of the canal, where civilians would have been stood close to the bomber at around 6pm local time (3pm BST).
It is suspected a second explosion may have been set off soon after the first, indicating multiple suicide bombers are targeting the evacuation effort.
People outside the airport had been advised to leave the area immediately as concerns of violence from an ISIS affiliate group grew.
The airport has become the focus of the evacuation of expats and Afghans and their families who have helped foreign troops, since the Taliban took control of the country last week.
Images from the scene shows people including children walking around in shock. People can be seen with visible injuries and blood.
Australia, the US and UK had all issued alerts to their citizens as of Thursday morning warning of a potential attack.
The Ministry of Defence has tweeted: "We are working urgently to establish what has happened in Kabul and its impact on the ongoing evacuation effort.
"Our primary concern remains the safety of our personnel, British citizens and the citizens of Afghanistan.
Earlier today, Prime Minister Boris Johnson said that the “overwhelming majority” of people eligible to be evacuated from Afghanistan have now been removed.
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 gun fire at northern gate of Baron's Hotel. Worried this will devastate evacuation - so many hurt. My heart is with all those injured and killed," she said.
Official figures suggest that over 100,000 people have now been evacuated from Afghanistan since the Taliban took control of the nation.
THIS IS A BREAKING STORY, PLEASE KEEP CHECKING FOR FURTHER UPDATES
