U.S. Marine Lt. Col. William R. Higgins has been killed by his pro-Iranian Shiite Moslem captors in south Lebanon, a Christian-controlled radio station reported Monday. The Beirut-based Voice of Lebanon of President Amin Gemayel's rightist Phalange Party said Higgins was "killed and buried by his captors" in the southern Lebanese village of Siddiqine. However, the Voice of Lebanon has a record of frequent inaccuracies on hostage affairs in Lebanon. Its Higgins report could not be independently verified. The radio said the killing took place hours before pro-Syrian militiamen of Justice Minister Nabih Berri's Amal movement captured Siddiqine from Iranian-backed Hezbollah supporters, apparently to keep Amal for claiming credit for his liberation.