(S (S (BASENP (NNS Sources)) (VP (VBD said) (SBAR (IN that) (S (BASENP (DT the) (NNP U.S.) (NNS forces)) (VP (VP (VP (VP (VP (VP (ADVP (RB first)) (VP (VP (VBD landed) (BASENP (PRPD their) (NNS helicopters))) (PP (IN around) (BASENP (DT the) (NN building))))) (COMMA ,) (VP (ADVP (RB then)) (VP (VBD broke) (PP (IN through) (NP (BASENP (DT the) (NN office) (POS 's)) (NN gate)))))) (COMMA ,) (VP (VBD disarmed) (BASENP (DT the) (NNS guards)))) (COMMA ,) (VP (VBD confiscated) (NP (BASENP (DT some) (NNS documents)) (CC and) (BASENP (JJ certain) (NNS objects))))) (COMMA ,) (VP (VBD arrested) (BASENP (NN five) (JJ suspected) (NNS terrorists)))) (CONJP (COMMA ,) (CC and)) (VP (ADVP (RB then)) (VP (VBD left) (PP (IN for) (BASENP (DT an) (JJ undisclosed) (NN location)))))))))) (PERIOD .))