4 American Troops Killed by Bomb in Afghanistan

NATO says four American troops have been killed in a roadside bomb explosion in eastern Afghanistan.

Tuesday's deaths come amid a particularly bloody period for American forces in the country, with 18 service members killed since Saturday to bring this month's total to 53. Another member of the international coalition whose nationality has not been released was killed on Monday.

July was the deadliest month for U.S. troops in Afghanistan since the 2001 invasion, with 66 killed.

Southern and eastern Afghanistan have seen the heaviest fighting. Those areas are also closest to the border with Pakistan, where the insurgents maintain training bases for recruits to be later infiltrated into Afghanistan.