"Trinamool has been doing lot of development, and in doing this positive development (in Bengal), Trinamool has made two-three mistakes and we will learn from these mistakes," he said.
Last week, the Trinamool denied that its activists forced their way into Kolkata's famous Presidency University and attacked students and teachers with javelins and sticks, while threatening women would be raped.
Today, Mr O'Brien said that if the party's workers were involved in the rampage, they will be punished. Referring to the chief minister, he said, "If there is violence, if there is hooliganism; she will not take tolerate it. And even if Trinamool workers are involved, that does not absolve them from the guilt."
The tension between Ms Banerjee's Trinamool and the Left - a constant worry for Bengal - peaked when a student activist from the Left was arrested during a demonstration in Kolkata on April 3 and died a few hours later. The Left said the 22-year-old was battered by the police. Ms Banerjee said the death was an accident and "a small and petty matter."
Ms Banerjee has also been seen as intolerant of dissent or criticism - a professor who posted cartoons of her on social networks was controversially arrested in 2012.
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