(S (S (S (BASENP (NNS Witnesses)) (VP (VBD reported) (S (VP (VBG hearing) (NP (BASENP (DT a) (NN number)) (PP (IN of) (NP (BASENP (JJ loud) (NNS explosions)) (CC and) (BASENP (JJ heavy) (NN gunfire))))))))) (SBAR (IN as) (S (BASENP (DT the) (NNS militants)) (VP (VBD continued) (S (VP (TO to) (VP (VB attack) (BASENP (DT the) (NN base))))))))) (PERIOD .))