WASHINGTON — August has proved the deadliest month for US forces in Afghanistan since the war began nearly 10 years ago, with the death toll at 66 troops, according to the Pentagon.

The downing of a Chinook helicopter by insurgents in eastern Afghanistan, in which 30 troops died -- including a unit of elite Navy SEAL commandos -- accounted for almost half the total.

The death toll surpassed the previous record of 65 killed in July last year, according to Defense Department figures as of Wednesday.

Homemade bombs planted by insurgents remain the leading cause of death for US and other foreign troops, amid elaborate efforts by the NATO-led force to detect the improvised explosives.

Despite the deployment of US and NATO reinforcements, the insurgency in Afghanistan has grown every passing year since it was launched by the remnants of the Taliban in late 2001, after their regime was toppled in a US-led invasion.

About 10,000 US troops are due to leave Afghanistan this year, part of a gradual drawdown through the end of 2014.

US President Barack Obama said in June another 23,000 American troops would leave Afghanistan by the end of next summer, leaving behind a 65,000-strong force and effectively ending a surge of troops ordered in late 2009.