"The action may include arresting concerned leaders in the backdrop of pressure building up from New Delhi", a senior official said.

"If at all arrests of top leaders are to be made, it will be from both the sides and not just from MNS", he said.

"In such a case, police monitoring the whereabouts of the concerned leaders would detain them and immediately produce them before the court to contain the fallout", the official said.

There was speculation that 39-year-old Raj Thackeray may be arrested in the wake of reports in a section of media that the Advocate General's office had informed the Home Department that there were sufficient grounds for his arrest.

Police have already taken into custody key aides of Raj.

"If any action is in the offing, it cannot be an one-off case and it would be against top figures of both the sides", the official said.

The war of words over Raj Thackeray's remarks against North Indians spilled onto Mumbai streets on Sunday with attacks against taximen and North Indian street vendors.

Chief Minister Vilasrao Deshmukh has said action would be taken against concerned leaders after the government takes legal opinion.