Only a forensic examination will reveal if the office was set on fire or a petrol bomb was hurled. It has suffered some damage, they said.
BJP workers alleged that the CPI-M was behind the attack.
The party called for a strike in Payyanur tomorrow. However, CPI-M workers alleged that BJP activists hurled three country bombs at a motorcycle rally taken out by them at Payannur in the evening on the first death anniversary of CPI-M worker Dhanraj who was killed allegedly by RSS activists on July 11 last year.
Four workers suffered minor injuries in the incident, the workers said.
Police said a few houses of workers belonging to both parties were attacked. Some persons have been taken into custody in connection with the incidents. The situation is under control, they said.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)