The incident occurred late last night when four assailants came in a car and hurled crude bombs and attacked S P Shuhaib and two other party members with machetes, they said.
Shuhaib, the Mattanur block Youth Congress secretary, was at a roadside tea shop at Therur with Riaz and Naushad when the attack happened.
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The critically-injured Shuhaib was rushed to the Indira Gandhi Co-Operative Hospital at Thalassery where he succumbed, police said adding that the injured persons were stable.
Police suspect it could be related to the incidents of violence in the area last week.
Cases under sections 307 (attempt to murder), 324 voluntarily causing hurt by dangerous weapons), 341 (punishment for wrongful restraint), 302 (read with 34) of the IPC and sections 3 and 5 of the Explosive Substances Act have been registered.
No one has been arrested in connection with the incident and further investigations were on, police said.
Meanwhile, the Congress has announced a dawn-to-dusk hartal in the district today against yesterday's attack.
Kannur in north Kerala has witnessed a series of political murders and violence after the Left Democratic Front (LDF) government came to power last year.