The move marks another setback for the ruling Trinamool Congress amid indications of growing internal discontent within the organisation.

'Only changed my room'

Speaking after joining the rebel camp, Mitra attempted to play down the significance of his decision, saying he had "only changed his room in the Assembly."

Despite the remark, he launched a sharp criticism of the party's leadership and alleged that the organisation had increasingly become centred around Trinamool Congress national general secretary Abhishek Banerjee.

Criticism of party leadership

Explaining his decision, Mitra claimed that he had previously advised Abhishek Banerjee to step away from active leadership temporarily to allow the party to reorganise.

"... I had suggested to Abhishek Banerjee that he step aside for six months or a year. I told him, let us build the party, and then you can come back and take your seat but he refused. He said, I won't leave the party. The party is sinking; the boat has gone under. People are dying. Yet, the party decided or rather it was forced to accept that everyone else could die, but Abhishek had to be saved. It is deeply saddening," Mitra said.

He further alleged that the party's focus had narrowed around a single leader.

"The party belongs to everyone, yet it seems to have been reduced to serving only Abhishek. I earnestly request Mamata ji to come; let us view this as a marathon. We will surely cross paths along the way. Let us see which horse surges ahead. I have resigned from all the positions. Though I remain an MLA. I have left everything associated with Trinamool. That means I am no longer a Trinamool MLA in the functional sense," he added.

Fresh political challenge for Kalighat TMC

Mitra's resignation and decision to align with the Ritabrata Banerjee-led rebel faction come at a time when the Trinamool Congress is facing signs of internal divisions.

While he has relinquished all organisational responsibilities within the party, Mitra said he continues to hold his position as a Member of the Legislative Assembly (MLA), although he no longer considers himself a Trinamool MLA in a functional capacity.

His departure adds to the political challenges confronting the ruling party as it seeks to manage dissent within its ranks.