(S (S (S (BASENP (DT The) (NNS explosions)) (VP (VBP are) (VP (VBN believed) (S (VP (TO to) (VP (VB be) (NP (BASENP (DT the) (NN result)) (PP (IN of) (NP (BASENP (DT a) (NN fire)) (SBAR (WHNP (WDT which)) (S (VP (VP (VBD broke) (PRT (RP out))) (PP (IN inside) (NP (BASENP (DT the) (NNP Forward) (NNP Operating) (NNP Base) (NNP Falcon)) (COMMA ,) (NP (BASENP (DT a) (JJ U.S.) (NNS ammunitions) (NN depot)) (PP (IN inside) (BASENP (DT the) (NN zone)))))))))))))))))) (CONJP (COMMA ,) (CC but)) (S (S (BASENP (PRP it)) (VP (VP (VBZ is) (RB not)) (VBN known))) (SBAR (IN if) (S (BASENP (DT the) (NN fire)) (VP (VBD was) (VP (VBN started) (PP (JJ due) (PP (TO to) (BASENP (DT an) (NN attack)))))))))) (PERIOD .))