KABUL, July 12 (Reuters) - A roadside bomb killed two U.S. Marines in southern Afghanistan, the U.S. military said on Sunday, the latest deaths in an escalation of violence that has put pressure on coalition leaders over their war strategy.

Thousands of U.S. Marines and hundreds of British soldiers have been fighting major new offensives in the past 10 days in Helmand province, a Taliban stronghold and Afghanistan's biggest producer of the opium that funds the insurgency.