A spokesman said the officer, who fled the scene and has yet to be found, was a member of their rebel organization, according to Sky News.
"It's a new Taliban tactic," he said.
"We have more Taliban who have infiltrated into the police and army."
Three soldiers from the Grenadier Guards and two from the Royal Military Police were fatally wounded during an attack following a patrol in the Nad-e'Ali district.
Six soldiers wounded in the incident are being treated at Camp Bastion, the Army's main Afghan base.