The so-called Islamic State group has released photos of weapons and kit belonging to US troops discarded after fighting in Afghanistan.
The photos include the ID cards of a soldier named Ryan Larson it obtained following clashes in Nangarhar province bordering Pakistan.
They show an American portable rocket launcher, radio, grenades and other kit not commonly used by Afghan forces.
The US has admitted the loss of weapons but insists no troops were captured.
“We are still working to determine if all of the equipment in the pictures was lost during recent operations or at some other time in the past,” Brig Gen Charles Cleveland told the BBC.
In an earlier statement on Sunday US military spokesman Commander Ron Flesvig said Specialist Larson had been “attached to a unit conducting a partnered [operation] with Afghan forces”.
“The loss of personal identification is unfortunate,” he added.
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A statement released on the IS-affiliated Amaq news agency did not specify when the photos were taken, or when the American equipment was seized.
Correspondents say there is much uncertainty surrounding the incident, including why US troops left the area so quickly and whether the strength of IS in the area was underestimated.
The US-based Founderscode.com website said that IS fighters seized the equipment after repelling a joint US-Afghan attack involving tanks and heavy air cover. An American flag was among the items seized, it says.
Image copyright AP
Image caption Afghan forces say they made gains against IS earlier this month in Jalalabad province east of Kabul
IS last month said that it was behind an attack attack on a protest march in the Afghan capital, Kabul that killed 80 people and wounded 230.
Afghan intelligence sources have suggested that the suicide bombers were sent from Nangarhar province to carry out the attack.
IS was known to have a presence in eastern Afghanistan but had not previously admitted carrying out assaults in the capital.
The Taliban and IS have been locked in frequent battles in Afghanistan since January 2015.