The Pentagon is investigating possible misconduct by the official in charge of accounting for missing U.S. military from previous wars, a defense official said on Tuesday.

The official did not provide details on the nature of the alleged misconduct but said the probe involved Jerry Jennings, deputy assistant secretary of defense for Prisoners of War/Missing Personnel Affairs, who is cooperating with the investigation.

Some U.S. activists in the field have criticized Jennings’ performance, accusing him of showing anger, hostility and disdain toward families of missing soldiers, and some groups have formally voted that they have no confidence in him.

Larry Greer, a Pentagon spokesman on POW/MIA issues, said Jennings is now on medical leave “but we all talk to him daily.”

Bryan Whitman, a Pentagon spokesman, said, “Jerry Jennings is in a tough job where emotions understandably tend to run high. He is completely committed to the mission of full accounting of our service members missing in action.”

Jennings, 65, has served in the post since August 2001. His office oversees missions in such countries as Vietnam, Laos and North Korea to recover the remains of missing American military personnel.

He is also the U.S. chairman of the U.S.-Russia Joint Commission on POW/MIAs.