The president of a little-known Hindu Samaj Party was murdered at his home in Khurshed Bagh under the Naka Hindola police station area here, police said on Friday.
Police have registered an FIR against three persons in this regard.
Kamlesh Tiwari (45) was earlier associated with a faction of the Hindu Mahasabha, the police said.
Late on Friday night, Additional Chief Secretary (Home) Awanish Awasthi said a special investigation team (SIT) had been constituted to probe the incident.
Awasthi said the team consisted of Inspector General (Lucknow) S K Bhagat, Lucknow Superintendent of Police (Crime) Dinesh Puri and STF deputy SP P K Mishra.
In a statement issued by the Uttar Pradesh government, Director General of Police (DGP) O P Singh said: "Tiwari was provided security for the past some months, under which apart from a gunner, a security personnel was provided from the local police station."
Elaborating on the registration of the FIR, Tripathi said, "On the basis of the complaint lodged by the wife of the deceased, police have registered an FIR against three people, including an unknown person."
They have been booked under Sections 302 (punishment for murder) and 120-B (punishment of criminal conspiracy) of the IPC."
UP DGP OP Singh told reporters, "Those who have murdered Tiwari are said to be his acquaintances. They spent over half an hour with him and even gave Tiwari a box of sweets and after it the murder took place. We have got some vital clues and based on CCTV footage and other evidences, we are working on the case."
When asked whether there was any possible terror angle in the incident, Additional Director General of Police (Law and Order) PV Ramasastry told PTI, "All the angles are being looked into. And, it would be improper to jump to any conclusion."
Earlier in the day, Tiwari's wife Kiran in a complaint to police said, "Around 12.30 pm, my husband was sitting in his office located on the first floor of the house and speaking to some unknown persons. I was in another room. Suddenly, for nearly 4-5 minutes, there was no conversation. I came out to enquire and saw my husband lying in a pool of blood. The two persons, who had come to meet him, were running out of the office."
She further alleged, "In 2016, Mohammed Mufti Naeem Kazmi and Imam Maulana Anuwarul Haq had announced a cash reward of Rs 1.5 crore on my husband's head. They have killed my husband by hatching a conspiracy."