At least four people were shot dead in West Bengal's Cooch Behar, where voting is happening for nine seats, in the fourth phase of state assembly elections on Saturday.
Indian news agency PTI reported that four people died as the Central Industrial Security Force allegedly opened fire after coming under attack from locals who "attempted to snatch their rifles".
According to NDTV, the Election Commission of India has sought a report into the incident.
In a separate incident of violence on Saturday, an 18-year-old man was killed after shots were fired during a clash between workers of the Bharatiya Janata Party and Trinamool Congress in the Pathantuli area of Cooch Behar.
The role of the federal security forces in the voting began to be scrutinised after West Bengal Chief Mamata Banerjee accused the federal government of using the federal security agencies against her party during voting. She alleged that the security forces were stopping people from voting in her party's favour at the polling booths.
Banerjee also called upon women in the state to "surround" federal security personnel if they indulged in unfair practices.
Senior leader of the Trinamool Congress Derek O'Brien responded angrily to Saturday's incidents in a series of tweets.
Immediately after the incidents, Derek O'Brien sent a letter to the Election Commission saying that those killed were Trinamool Congress workers "shot dead by the CRPF after BJP captured the booth".