Seeing red over the apparent bonhomie between Prime Minister Narendra Modi and West Bengal Chief Minister Mamata Banerjee, the Congress and the CPI-M on Sunday charged the BJP and the Trinamool Congress of cosying up each other to suit mutual political interests.

Referring to Modi's address at an event in Burdwan district where the prime minister made a veiled attack on the Congress over scams, the Congress and the Communist Party of India-Marxist charged him of going soft on the Trinamool, several of whose leaders are being investigated for the multi-crore rupee Saradha scam.

"An unholy nexus has developed between Mamata and Modi. If Mamata wants to save herself from the CBI probe in Saradha, Modi wants to pass anti-people bills in parliament," said state Congress president Adhir Ranjan Chowdhury.

Chowdhury, who led a rally in the city against the "unholy nexus", also charged the Bharatiya Janata Party which rules at the centre, of going cold on the Central Bureau of Investigation (CBI) probe into the Saradha scam.

"The CBI probe in Saradha is already in the cold. Modi has gone silent on Saradha. He did not even utter anything on the Burdwan and Pingla blast," said Chowdhury referring to the twin blasts in the state.

Far away from days of high-octane and often spiteful verbal duels, there was apparent camaraderie between Banerjee, also the Trinamool chief and Modi since his arrival in the state Saturday for the first time after taking over as the prime minister.

Besides attending an event in the city where Modi launched three social security schemes, Banerjee Saturday met the prime minister at the Raj Bhavan urging complete waiver of the state's debt burden.

She was also present at Burnpur in Burdwn district on Sunday where Modi inaugurated the upgraded IISCO Steel Plant (ISP). 

Addressing the event, Modi referred to political attacks during the build up to the Lok Sabha polls last year. 

"During the build up to the Lok Sabha polls, all political parties were attacking each other. I too came to Bengal and attacked and others too attacked me," said Modi who as BJP prime ministerial candidate had taken the attack to Banerjee over the Saradha issue.

"But during February, March and April (2014), the only news that came was scams. Coal scam, spectrum scam, submarine scama scam in air, water and land," he said.

CPI-M affiliated Centre of Indian Trade Unions (CITU) state president Shyamal Chakraborty charged the BJP of cosying up to the Trinamool for its support in parliament.

"Modi talked about so many scams but how can he forget the Saradha scam which has been hogging the headlines. He is now bargaining with Mamata. Whenever going gets tough for Modi in parliament, Trinamool comes to the rescue either by walking out or extending support," he said.

"Earlier Modi used to say 'bhag Mamata bhag' (run, Mamata run). But now it has turn into 'let's walk together hand in hand'," added Chakraborty. 

State BJP president Rahul Sinha defended Modi's stand citing political courtesy.

"Criticising the state government, in front of the chief minister who is an invitee, goes against political courtesy. BJP is trying to create a new political culture and that has reflected in Modi's address where he talked about improved centre-state relations," he said, but warned of Modi coming back to his attacking ways during his next visit.