(S (S (BASENP (PRP It)) (VP (VBZ is) (VP (VBN believed) (S (VP (TO to) (VP (VB be) (NP (NP (BASENP (DT the) (JJ first) (JJ serious) (NN attack)) (PP (IN of) (BASENP (DT the) (JJ separatist) (NN group) (NNP ETA)))) (SBAR (IN since) (S (BASENP (PRP it)) (VP (ADVP (RB unilaterally)) (VP (VP (VBD ended) (BASENP (DT a) (NN cease-fire))) (PP (IN in) (BASENP (NNP June)))))))))))))) (PERIOD .))