Police identified the victim as E Manoj, a local office-bearer of RSS. The gang waylaid Manoj on a road, threw a country-made bomb at him and then hacked him to death before fleeing the area.
RSS-BJP leaders alleged that the CPI(M) was behind the killing and called for a dawn-to-dusk hartal in the district tomorrow.
The area, which was witness to violence involving RSS and CPI(M) workers in the past, has been remaining largely calm in the last few years.
But tension resurfaced with the BJP and CPI(M) poaching workers from each side in recent times, police said.
Last year, a large number of BJP workers led by a prominent local leader had joined the CPI(M).
In retaliation, the saffron party lured scores of CPI(M) workers to its camp last month.