With a total of 22,000 U.S. troops deployed in Afghanistan by May 2006, the U.S. joined in the ISAF lead Operation Mountain Thrust. In the attempt to quell the Taliban insurgency in southern Afghanistan, more than 1,000 insurgents and 150 ISAF troops were killed in the two-month operation, being the bloodiest period since the start of the war in 2001. With ISAF assuming complete command of security forces in Afghanistan in October 2006, the U.S. saw mounting skepticism from European allies over the war at the 2006 Riga summit. U.S.-Afghan diplomatic relations began to flare after the August 2008 Azizabad airstrike in Herat Province, which killed 91 civilians, including 60 children and 15 women. The attack sparked protest over "collateral damage"; with a 40% increase in civilian deaths in 2008.