A middle-aged BJP worker was found hanging outside a village in West Bengal's Paschim Medinipur district on Monday evening, around 24 hours after he went missing, police said.
The BJP alleged that criminals of the Trinamool Congress murdered Bacchu Bera. The ruling party, however, denied the charge.
"We have started an investigation into the case. No arrests have been made," a police officer said.
Police said that Mr Bera had gone missing in Sunday afternoon and he was found hanging from a tree near his village in Datan area on Monday evening.
The state BJP unit blamed the ruling TMC for the death of its activist.
"Our party worker Bachhu Bera was murdered by TMC goons. We want justice. He was missing since last evening, and today he was found hanging from the tree. We condemn violence," state BJP president Dilip Ghosh said in a statement.
The Bengal BJP in its Twitter handle also condemned the incident.
"Political murder continues in Bengal! Bachhu Bera, BJP worker from Datan, Medinipur was brutally murdered. On this auspicious day of Bijoyadashami we are sure good will win over Evil, in the Land of Maa Durga," the state BJP tweeted.
"These Evils will be eradicated from this pious land" next year, it said.
Assembly elections in the state are likely to be held in April or May next year.
The district BJP unit, however, dubbed the allegations as baseless and politically motivated.
"We heard that the person who died was mentally unstable and was a drug addict. Let the police investigate the matter. We criticise the attempt by the BJP to politicise every death," TMC West Midnapore district president Ajit Maity said.
The body was sent for post-mortem examination.