TEHRAN, Iran (AP) -- A former U.S. Marine interpreter arrested while on a trip to visit his Iranian grandmothers has been sentenced to death as a CIA spy, state radio reported Monday, in a case likely to become a new flashpoint in the escalating tensions between Tehran's defiance over its nuclear program and Washington's efforts to impose more crippling sanctions.It was the first time an American citizen has been sentenced to death in Iran since the 1979 Islamic Revolution, according to the International Campaign for Human Rights in Iran.\We are seriously concerned regarding the death sentence