The explosion occurred at one of the entrances of Hamid Karzai International Airport and appeared to be a suicide attack, according to three US officials.
Crowds of Afghans have gathered at the gates to try to get into the airport, which has become the country’s only exit since the Taliban took Kabul.
A US official said there were Afghans injured, but there was no word yet on American casualties.
Pentagon spokesman John Kirby confirmed there was an explosion outside the airport. “We can confirm an explosion outside Kabul airport. Casualties are unknown at this time. We will provide more details when possible,” he said in a tweet.
Top US diplomat in Kabul, Amb. Ross Wilson, said on Thursday that he could not find out the specifics of the security threat outside the gates of Kabul airport cited in an embassy warning, but noted that “it is clear considered credible, imminent, attractive.”
US President Joe Biden was briefed on the explosion outside Kabul airport, a White House official said.
A UK government spokesman said the government was “working urgently to determine what happened and its impact on the ongoing evacuation effort.”
“Our primary concern remains the safety of our staff, British nationals and Afghan nationals. We are in close contact with the United States and other NATO allies at the operational level. for an immediate response to this incident.”
This is an evolving story.
CNN’s Jeremy Diamond, Jim Sciutto and Lauren Moorhouse contributed to this report.
