RJD supremo Lalu Prasad on Monday termed the arrest of a Jadavpore University professor for posting a cartoon on West Bengal Chief Minister Mamata Banerjee as an assault on the freedom of expression.

"People make my cartoons to which I have never objected.

It is an assault on the freedom of expression," the former Bihar chief minister told reporters here.

"I strongly condemn it. Something very bad has taken place in West Bengal," he said.