Two soldiers shot dead in southern Afghanistan by local police officers were British, the Ministry of Defence confirmed on Sunday a day after the killings.

"Sadly, it is my duty to confirm that a soldier serving with 1st Battalion Welsh Guards and an airman from The Royal Air Force have been shot and killed in the Lashkar Gah district of Helmand province," said Major Ian Lawrence, spokesman for Task Force Helmand.

The ministry said in a statement that the two were "shot and killed by members of the Afghan police force", although NATO's force in Afghanistan had on Saturday indicated they were insurgents dressed as police.

A police spokesman said they were members of the force, however, and a senior security official in the province said they had been in the Afghan police force for about a year.

The two had been working as part of an advisory team and were providing security for a meeting with local officials at the time, the ministry's statement said.

ISAF said Saturday that one of the attackers had been killed and the other was still being sought.

The killings bring this year's toll in "green-on-blue" attacks -- in which Afghan forces turn their weapons against their Western Allies -- to 22, in a total of 16 such incidents.

An increasing number of Afghan troops have turned their weapons on NATO soldiers who are helping Kabul fight a decade-long insurgency by hardline Taliban Islamists.

Some of the assaults are claimed by the Taliban, who say they have infiltrated the ranks of Afghan security forces, but many are attributed to cultural differences and antagonism between the allied forces.

ISAF has taken several security measures in response to the shootings, including assigning "guardian angels" -- soldiers who watch over their comrades as they sleep.

The families of the two British soldiers have been informed, the ministry said.

The killings bring the British toll in the more than 10-year Afghan war to 412.

Britain has some 9,500 troops in Afghanistan, mainly based in Helmand.

They form part of a 130,000-strong ISAF force fighting alongside some 350,000 Afghan security personnel against the Taliban-led insurgency, but the foreign troops are due to pull out of the country in 2014.

Two other NATO soldiers died Saturday, one in a bomb blast and the other as a result of a "non-battle related injury", ISAF said, without giving the nationalities of any of the victims.