NATO said an explosion Wednesday in southern Afghanistan killed two of its troops and wounded six others.

The military alliance did not reveal the troops' nationalities or the exact location of the blast.

Thousands of U.S. soldiers and Marines have joined British, Canadian and Dutch troops in southern Afghanistan — the center of the Taliban-led insurgency — in an attempt to reverse militant gains of the last three years.

NATO has about 58,000 soldiers in Afghanistan, including 26,000 Americans, and another 12,000 more U.S. troops are serving under a separate command.

President Barack Obama is deploying 21,000 additional U.S. forces to confront the Taliban more forcefully, particularly in the south where the insurgency is strongest.