Four US troops killed by Afghan bomb

Four US soldiers were killed by an improvised explosive device in southern Afghanistan today.

Their deaths bring to 41 the number of US troops killed in Afghanistan this month, the second deadliest month in the country since the 2001 US invasion. Last month a record 44 US troops died.

Violence has peaked the last three years, and the US has more than 60,000 forces in the country, a record number.