Kabul, Afghanistan ? An insurgent attack on a British base killed two soldiers and an Afghan interpreter, military officials said Sunday, while at least 20 militants died during clashes and coalition airstrikes.

A U.S. helicopter crashed in an accident in southern Afghanistan, killing one crew member, the U.S. military said.

The deaths came amid a massive anti-Taliban campaign in southern Afghanistan involving more than 10,000 Afghan and coalition soldiers. It is the largest military offensive since the hard-line regime’s ouster in late 2001.

The two British soldiers died after their base was hit by small arms fire and rocket-propelled grenades Saturday night in southern Helmand province, said military spokesman Capt. Drew Gibson.

Two British soldiers were killed last week in an attack in the same district of Helmand province. A total of five British troops have been killed since the start of Operation Mountain Thrust.