(S (S (BASENP (DT The) (NN attack)) (VP (VBZ has) (VP (VBN been) (VP (VP (VBN blamed) (PP (IN by) (BASENP (JJ regional) (NNS authorities)))) (PP (IN on) (BASENP (JJ Islamist) (JJ separatist) (NNS rebels))))))) (PERIOD .))