(S (S (S (BASENP (DT The) (NN blast)) (VP (VBZ comes))) (SBAR (IN as) (S (BASENP (DT the) (NNP United) (NNPS Nations)) (VP (VBD announced) (SBAR (S (BASENP (PRP it)) (VP (VBD was) (VP (VP (VP (VBG withdrawing) (BASENP (PRPD its) (JJ international) (NNS staff))) (PP (IN from) (BASENP (JJ northwestern) (NNP Pakistan)))) (PP (JJ due) (PP (TO to) (BASENP (NN security) (NNS concerns)))))))))))) (PERIOD .))