The offences are cognisable and non-bailable as pressure mounted on the Maharashtra Government to take action against the Maharashtra Navnirman Sena (MNS) leader for his anti-North Indian diatribe that triggered street violence early last week.

Appearing to be even handed on the line of action, the police also slapped a case against Samajwadi Party leader Abu Asim Azmi amid trading of charges between MNS and the SP on what led to trouble in the country's commercial capital.

Joint Commissioner of Police (Law and Order) K L Prasad said arrests are mandatory in the type of cases registered against Thackeray and Azmi but gave no time-frame.

"There was enough evidence to register cases against Raj and Azmi...if the Investigating Officer feels that arrest is warranted then we will take necessary action," Prasad told reporters.

The case against Raj was registered at the suburban Vikhroli police station last night while the FIR was filed against Azmi at the Shivaji Park police station, Deputy Commissioner of Police (Zone VII) D Karale said.

Raj was booked under sections 153 (wantonly giving provocation with intent to cause riot), 153 A (promoting enmity between groups on the basis of place of birth, residence, etc) and 153 B (imputations, assertations prejudicial to national integration). Azmi was also booked under identical charges.