Three people have died and 13 have been injured in an explosion at a US base in Afghanistan.
The blast occurred just after 5.30am local time at the NATO air base at Bagram, around an hour north of the Afghan capital Kabul.
The NATO-led Resolute Support mission said force protection and medical teams were responding but gave no additional information.
NBC News reported that it was a suicide bomber. An official said he detonated the vest while people were gathering for a post-Veterans Day fun run.
Sources said he chose the time and location to inflict the most damage possible.
Abdul Shokor Qodosi, the district governor of Bagram, said that at least three people were killed and 13 injured in the blast, which he said occurred near a dining facility.
He said the cause of the blast was unclear.
There has been a recent spate of attacks in the area.
Bagram is the largest US military base in Afghanistan. Many of the buildings have been torn down in a bid to stop the Taliban taking anything when the troops leave.
It used to be the site of the US’ biggest military prison, but was closed in December 2014.