(S (S (S (BASENP (NN Opposition) (NNS groups)) (VP (VBD asserted) (SBAR (IN that) (S (BASENP (DT the) (NNS elections)) (VP (VBD were) (VP (VBN rigged) (S (VP (TO to) (VP (VB favor) (BASENP (NN president) (NNP Mahmoud) (NNP Ahmadinejad))))))))))) (CONJP (COMMA ,) (CC but)) (S (BASENP (DT the) (NN government)) (VP (VP (VBD denied) (BASENP (PRP it))) (COMMA ,) (S (VP (VBG saying) (SBAR (S (BASENP (PRP it)) (VP (VBD was) (NP (BASENP (DT a) (JJ foreign-backed) (NN attempt)) (SBAR (S (VP (TO to) (VP (VB discredit) (BASENP (DT the) (JJ Iranian) (NN government) (NN system))))))))))))))) (PERIOD .))