The defeat "does not reflect the mood of the common man," he said in a statement last night.
"This was virtually a victory of Prabhunath Singh (RJD candidate) who has represented the constituency three times in the past," he said.
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Modi, who is senior BJP leader in Bihar, said though defeat in Maharajganj bypoll was not a cause of tension but still "it will be reviewed by the NDA leaders."
He also reiterated the point made by Chief Minister Nitish Kumar that NDA had fared badly in by-elections for 18 Assembly seats in 2009 during earlier NDA rule in the state but bounced back to a record victory in the 2010 Assembly elections.
"NDA will achieve a big win in the coming Lok Sabha elections in 2014," Modi, an architect of NDA alliance in Bihar along with the CM, said.
The Bihar Deputy Chief Minister greeted Gujarat Chief Minister Narendra Modi for impressive victory in bypolls held in his state.