A man wearing an Afghan police uniform has shot and killed two British soldiers in southern Afghanistan, in the latest apparent “insider” attack.

The British Defense Ministry said the attack took place Tuesday at a checkpoint in the Nahr-e-Saraj district of Helmand province. The ministry said the “loss of these soldiers is a huge blow to the Royal Gurkha Rifles and everyone serving in Task Force Helmand.”

NATO gave few details, but coalition spokesman Brigadier General Gunter Katz said the attacker “is trying to flee from that area, but he is being pursued by ISAF forces and by Afghan national security forces.”

The incident is the latest of several such attacks that threaten to seriously undermine trust between NATO and their Afghan counterparts, as foreign combat troops prepare to withdraw from Afghanistan by the end of 2014.

At least 53 coalition service members have been killed this year by Afghan soldiers and police or militants disguised as security personnel. NATO commanders have attributed a quarter of the so-called “insider” attacks to Taliban infiltration.

Coalition spokesman Katz said Tuesday, “it is very clear that nobody is able to put a wedge between the ISAF forces and the Afghan forces and our campaign will not be affected by these incidents.”

Separately, Afghan election officials say the country's next presidential election will take place on April 5, 2014.

The country's Independent Election Commission announced the date Tuesday, which was given as “Hamal 16, 1393,” according to the Islamic calendar.

President Hamid Karzai is serving his second term and is constitutionally barred from running for re-election.

The upcoming vote is seen as a test of Afghanistan's young democracy, after the 2009 election was marred by allegations of voter fraud.