KABUL (Reuters) – A bomb attack in western Afghanistan on Thursday killed three foreign troops from the NATO-led International Security Assistance Force (ISAF), the alliance said.

ISAF did not immediately provide further details on the nationalities of the casualties or on the attacks. Troops from the United States, Italy, Spain and Lithuania are based in western Afghanistan.

At least 35 foreign troops have died in Afghanistan this month alone.

Violence in Afghanistan is at its highest levels since the overthrow of the Taliban in late 2001, with rising casualties on all sides of the conflict. More than 2,000 foreign troops have died since then, more than half in the last two years.

Six foreign troops were killed in three attacks in the east and south of the country on Wednesday.

The rise in troop deaths will weigh heavily on U.S. President Barack Obama and his administration ahead of a review of the war in Afghanistan in December.

There are nearly 150,000 foreign troops in Afghanistan, including 100,000 Americans. Obama ordered an extra 30,000 U.S. troops to Afghanistan in December to try and quell the violence but plans to start withdrawing forces from the middle of 2011.