Trinamool Congress leader Mamata Banerjee on Monday appealed to Prime Minister Manmohan Singh to see to it that the CBI, under pressure from the Left parties, does not close important cases they are probing in West Bengal.

Banerjee, who recently signaled her break with the BJP in West Bengal, sought to turn the heat on the CPI(M) by taking up the theft of Rabindranath Tagore’s Nobel medallion from Shantiniketan and the Singur and Nandigarm issues with Prime Minister Manmohan Singh. She pleaded to Singh not to give in to Left pressure.

The Trinamool chief’s 15-minute meet with the Prime Minister comes amidst a narrowing gap between her party and the Congress. Banerjee, according to sources, is waiting for the UPA and the Left to severe all ties before she joins hands with Congress to take on the Left.

Considering the manner in which important cases concerning West Bengal have been tackled, sources said Banerjee feels that the CBI’s credibility had suffered a serious blow. She also sought to dispel the the Singh’s impression that tension in Nandigarm and Singur has died down.

Banerjee also announced her resignation from the governing body of Vishwa Bharati University to protest against the closure of the theft case. She said: “I cannot keep quiet, especially when there is a perception among the people that the case has been closed due to pressure from the Left Front Government. It is a shame that we cannot preserve the honour of our country.”