Mamata Banerjee on Wednesday announced she would not attend Prime Minister Narendra Modi’s swearing-in, a day after saying she would be at Thursday’s ceremony as a matter of “constitutional courtesy”.

The chief minister linked her latest decision to the BJP’s move of ferrying to the event the families of its Bengal workers who it claims were killed by Trinamul.

Trinamul sources said this was a “below-the-belt” attempt to humiliate Mamata before a pan-Indian audience at an event she had been invited to.

“The oath-taking ceremony is an august occasion to celebrate democracy, not one that should be devalued by any political party,” Mamata tweeted at 2.18pm.

“Congratulations, new Prime Minister, Narendra Modi Ji. It was my plan to accept the ‘Constitutional invitation’ and attend the oath-taking ceremony. However, in the last one hour, I am seeing media reports that the BJP are claiming 54 people have been murdered in political violence in Bengal.

“This is completely untrue. There have been no political murders in Bengal. These deaths may have occurred due to personal enmity, family quarrels and other disputes; nothing related to politics. There is no such record with us. So, I am sorry, Narendra Modi Ji, this has compelled me not to attend the ceremony.”

On Tuesday evening, Mamata had told journalists she had spoken to “some other chief ministers” and decided to attend Modi’s swearing-in “as a part of constitutional courtesy”.

Sources said she changed her mind after learning that the BJP planned to take the families of at least 40 of its slain workers by train to Delhi for the swearing-in.

BJP national general secretary Kailash Vijayvargiya accused Mamata of “looking for excuses” to stay away.

The BJP accuses Trinamul of murdering 80 of its workers in Bengal. Modi and BJP chief Amit Shah referred to the alleged violence repeatedly during the campaign, and even during the victory celebrations.

Trinamul sources said that if the BJP was sincere about showing respect to the families of victims of political violence, it should have also invited the families of the dozens of Trinamul workers they said were killed by the BJP.

“In the past year, most victims of political violence in Bengal have been Trinamul workers, killed in attacks by the BJP,” a Trinamul politician said.