NATO reported that four American troops were killed by a roadside bomb in Afghanistan Tuesday, bringing to 18 the number of U.S. soldiers killed since the weekend. The particularly bloody period for American forces has raised to 53 the total killed in August, one of the deadliest months for U.S. troops there since 66 were killed in 2001. The spike in US troops to over 120,000 has meant increased fighting and strikes on the U.S. forces. Most of the fighting is focused in southern and eastern Afghanistan, areas closest to the border with Pakistan, where insurgents train and launch raids into Afghanistan. U.S. commander Gen. David Petraeus has announced plans to “thin out” areas of the country as they are pacified.