"Our thoughts and prayers are with the families and friends who mourn their loss."

A US defence official said at least one attack was followed by a gun battle with Taliban fighters.

The deaths bring to 55 the number of US troops killed in October in Afghanistan.

The previous record high was in August, when 51 US soldiers died as Afghanistan held the first round of its presidential election. The Taliban had threatened to disrupt the poll, which has now gone to a second round run-off after widespread fraud was revealed.

The deadliest month for US troops in Iraq was November 2004, when 137 US soldiers were killed during the assault on the city of Fallujah.

Tuesday's deaths followed one of the worst days of the war for US forces in Afghanistan since they launched air attacks in 2001 to overthrow the then Taliban government.

Helicopter crash

On Monday, a US military helicopter crashed returning from the scene of a firefight with suspected drug traffickers in western Afghanistan, killing 10 American service personnel.

In a separate crash the same day, four US troops were killed when two helicopters collided over southern Afghanistan.

Military officials insisted that neither crash was the result of hostile fire, although the Taliban claimed they shot down a US helicopter in the western province of Badghis.

Afghanistan is the world's largest producer of opium - the raw ingredient in heroin - and the illicit drug trade has become a source of funding for the Taliban.