An explosion has taken place outside Kabul airport amid the evacuations of thousands of people from Western nations, the Pentagon has said.
The press secretary said the number of casualties was unclear.
The White House said President Joe Biden has been briefed on the explosion.
Live updates on the situation in Afghanistan as the evacuation continues
Sky News correspondent Sally Lockwood said the explosion occurred near the Baron hotel, where British troops and journalists have been staying.
Sky News chief correspondent Stuart Ramsey said his sources have told him the explosion was caused by a suicide bomber blowing himself up in a canalway.
He added: “We’re not certain on the number of casualties, we have to assume a number of civilians, but initial report suggests to us that American soldiers, not British soldiers but American soldiers have been injured.
“We’ve heard of fatalities but we haven’t been able to confirm that at this stage.”
The explosion came after warnings earlier in the day that a “very lethal” terror attack could occur at the airport in a matter of hours.
Conservative MP for Wealden, Nusrat Ghani, said on Twitter that she was on the phone to “an Afghan outside the airport when he heard the explosion.”
She added: “Praying that he gets away safely and we get his family safe passage out of this nightmare”.
The UK, the US and other nations have been moving to end the evacuations of tens of thousands of citizens ahead of the 31 August deadline.