Kabul, Afghanistan (CNN) -- A gunman in an Afghan Border Police uniform who killed six U.S. troops was a reliable officer who had been with the force for three years, a senior official said Wednesday.
But the Taliban claimed that Hezatullah had been a member of the militant group who joined the border police precisely to launch an attack on U.S. forces.
Six U.S. troops died Monday when a gunman opened fired on NATO-led service members, the Pentagon said.
Hezatullah, a 23-year-old who goes by one name, was a trusted member of the border police and had been receiving training from coalition forces, said Aminullah Amarkhil, commander of the border police in eastern Nangarhar province.
"Afghan and NATO forces have launched a joint investigation into this incident, and preliminary reports suggest that there is no reason to believe that Hezatullah was not trustworthy," Amarkhil said.
But Taliban spokesman, Zabiullah Mujahid, claimed responsibility for the attack and said Hezatullah had been planning such an assault all along.
"He has been waiting for the right moment, and now he finally achieved his goal." Mujahid said.
CNN could not independently confirm the Taliban claim.
The shooting broke out during a training mission in eastern Afghanistan, the International Security Assistance Force said in a news release. A joint Afghan and ISAF team is investigating.
The suspect also was killed in the incident, the ISAF said.
Spokesman David Lapan confirmed the deaths, and said no names are being released pending notification of the families.