President of Nepal's Hindu Youth Association, Kashi Nath Tiwari, was shot dead by three unidentified motor-borne masked assailants near his house in Birgunj district, police said in Kathmandu.
He breathed his last at the Narayani Sub-regional hospital after the attack on Saturday night.
He was attacked at Ashok Batika near his house, the police said, adding, no one has so far claimed responsibility for the attack.
Tiwari is said to have led a retaliation group against the Maoists when the former guerillas imposed an indefinite general strike in the country in the first week of May.
Angry supporters shut down the market in Birgunj to protest against the killing.
In a separate incident, a bank manager who was abducted by an armed group was released 34 days after his abduction.
Bishwonath Adhikari, manager of Madhyamanchal Rural Development Bank in Dhading district was found in an unconscious state late last night in Chitawan district.
He was abducted from Gajuri on May 23 by a group called Nepal Democracy Security Force. He was released after his family paid a ransom of Rs. 600,000, according to media reports in Kathmandu.
Local human rights activists found him lying unconscious under a bridge with his hands and feet tied, hours after paying the ransom.