Arrests are mandatory in cases registered against Maharashtra Navnirman Sena chief Raj Thackeray and Samajwadi Party leader Abu Asim Azmi, a top police official said on Monday.

Both the offences were cognisable and non-bailable and investigations are on in the matter, Joint Commissioner of Police (law and order) K L Prasad said.

Prasad, however, declined to disclose as to when the arrests would be made.

Police has filed a case against Raj Thackeray for "promoting" enmity between groups. Raj Thackeray has been booked for wantonly provoking with an intent to cause riot and promoting enmity between groups.

Raj Thackeray and Azmi have been 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, assertions prejudicial to national integration).

Azmi allegedly made provocative speeches at the Samajwadi Party rally held at Shivaji Park on February 3.