Officials say two Afghan civilians were killed and 21 wounded when a suicide bomber detonated explosives near a group of American troops. U.S. military spokeswoman Lt. Cmdr. Christine Sidenstricker confirms that an explosion has taken place against U.S. troops in Zabul province. She says there is no report of U.S. deaths. The top Afghan official in Zabul's Shah Joy district says a suicide bomber attacked the troops while they were walking in a market. Abdul Qayum says the blast killed two Afghans and wounded 21. A Taliban spokesman claimed responsibility for the attack and said the bomber was on a motorcycle. August is already the deadliest month of the eight-year Afghan war for U.S. troops. Forty-five have died. 