NATO says a man wearing an Afghan police uniform has shot and killed two coalition troops in southern Afghanistan in the latest apparent “insider” attack.

The international coalition did not give further details, but Afghan officials said the attacker killed two British soldiers Tuesday in Helmand province.

The incident is the latest in a series of such attacks that threaten to seriously undermine trust between NATO and their Afghan counterparts, as foreign combat troops prepare to complete their withdrawal 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.

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.