The ministry on its website said the two attached to the 1st Battalion of the Royal Gurkha Rifles were killed Tuesday at a checkpoint in the Nahr-e Saraj district of southwestern Helmand province, the country's opium-producing capital and once a Taliban stronghold.
Maj. Laurence Roche with the British task force in Helmand said the soldiers were killed "by a man wearing Afghan police uniform," adding their loss "is a huge blow to the Royal Gurkha Rifles and everyone serving in Task Force Helmand."
So-called green-on-blue killings by Afghans in police or military uniforms serving alongside coalition forces or by Taliban infiltrators have become a major threat to U.S. and NATO Forces as they fight the Taliban insurgency in Afghanistan.
A total of 56 international forces have died in such killings this year, the BBC reported.
Damian Collins, Conservative member of British Parliament from Folkestone and Hythe, where the Gurkha regiment is based, told the BBC, "It is terrible news and everyone in Folkestone will be saddened to hear it."
He said his community is proud of the Gurkhas.
The BBC quoted the Taliban as saying the killer was back with them after having infiltrated the Afghan police. Afghan and international security forces were reported to be looking for the attacker.
Col. Richard Kemp, a former commander in Afghanistan, said it would be impossible to completely stop such insider attacks, the BBC reported.
"There is no way of ensuring they won't happen, in the same way as there is no way of ensuring that attacks from outside won't happen either. It illustrates the 360-degree threat that our troops face day in and day out," he told the BBC.
While security for the international forces has been tightened, NATO has planned to continue to work with the Afghans as it prepares to withdraw most of its combat forces by end of 2014.