Four foreign troops have been killed in southern Afghanistan by attackers wearing local police uniforms, the International Security Assistance Force reported on Sunday.

The troops died "following an insider attack suspected to involve Afghan police,” ISAF said in a statement. It did not specify the location of the attack or the nationalities of the dead.

More than 50 foreign troops have been killed in so-called green-on-blue attacks since the beginning of the year.

The latest attack follows close on the heels of another that killed two British troops in Helmand Province. The soldiers died after being shot by a gunman wearing an Afghan police uniform, the British Defense Ministry announced on Saturday.

The international coalition in Afghanistan has lost more than 330 troops killed so far in 2012, according to ISAF information. The foreign troop contingents are scheduled to withdraw by the end of 2014.