State BJP president Nityanand Rai had said at a rally earlier Friday that "if Sarfaraz (RJD candidate) wins this election, Araria will become a safe haven for the ISIS. The victory of our candidate Pradip Singh will, on the other hand, give rise to patriotic fervour".
Mr Rai had also attacked the Lalu Prasad-headed RJD for its "failure to speak up against those indulging in cow slaughter...".
The comments came on the last day of campaigning for the by-elections, which has been necessitated by the death of Sarfaraz's father Taslimuddin.
Terming Mr Rai's remarks as "outrageous", RJD national vice president Shivanand Tiwary told PTI that the statement shows the "desperation in the BJP, which is faced with the possibility of a defeat in Araria".
Voting will be held for the Araria Lok Sabha seat, along with Jahanabad and Bhabhua Assembly segments on March 11.