A Samajwadi Party leader was shot dead in Mau district of Uttar Pradesh on Tuesday by unidentified persons.
The incident has triggered protests by party workers who fought a pitched battle with the police.
The assailants shot and killed SP's youth wing district president Amar Nath Yadav when he was coming out of the party office in Bal Niketan Tiraha area, police said.
The borders of the town have been sealed and a massive manhunt has been launched to nab the culprits.
The SP leader allegedly had a criminal past and old enmity could be the reason behind the killing, police said.
Yadav's murder triggered strong protests from the SP workers, who led by party parliamentarian Chandradeo Rajbhar, blocked traffic on the main road and also indulged in stone pelting.
Police resorted to cane-charge to disperse the mob in which several persons injured.
Security personnel in strength have been deployed to maintain law and order in the town, sources said, adding that the situation was tense but under control.