Four people have been killed in political unrest after Indian Prime Minister Narendra Modi’s Hindu-nationalist party celebrated victory in state polls in West Bengal, police and party officials said on Wednesday.

Modi’s Bharatiya Janata Party (BJP) swept polls in the key eastern state of more than 100 million people, winning 206 of the 294 assembly seats, according to results announced on Monday, for its first-ever victory in West Bengal.

West Bengal had been ruled by Modi’s fierce critic and adversary Mamata Banerjee as chief minister since 2011.

Banerjee, leader of the regional All India Trinamool Congress (TMC), also lost her seat in the polls and has rejected the results.

Police said clashes between rival party supporters erupted in the state capital Kolkata after results were announced on Monday.

Analysts say the BJP’s victory in the largely Bengali-speaking state is one of its most significant since Modi was first elected prime minister in 2014, expanding its dominance beyond the Hindi-speaking heartland of north and central India.

The BJP said two party workers were killed, while the TMC said two of their workers were beaten to death.

“Two of our workers were killed after results of the elections were announced on Monday,” BJP state leader Samik Bharracharya told AFP, insisting that the party is “for peace”.

TMC, in a statement on social media, reported the “brutal murder” of two party workers.

“Our party offices were attacked in several areas of the state,” TMC spokesman Narendranath Chakrabort told AFP. “Two of the victims were grassroots political workers.”

A senior police officer, who was not authorised to speak to reporters, confirmed four deaths in clashes and said one officer had been shot in the leg.