Haryana Police on Thursday said they are verifying a post on social media, purportedly by UK-based gangster Kapil Sangwan, claiming responsibility for the killing of Indian National Lok Dal's state unit chief Nafe Singh Rathee.

Rathee and Indian National Lok Dal (INLD) worker Jai Kishan were killed when unidentified assailants sprayed their vehicle with bullets in Jhajjar's Bahadurgarh on Sunday. The attack, which came ahead of the Lok Sabha polls, drew sharp reactions from the opposition parties in the BJP-ruled state.

Jhajjar police said they are verifying the social media post, purportedly by Sangwan, claiming responsibility for the killing. The post also claimed that Rathee had a close friendship with Sangwan's rival gangster.

"We are verifying the post and claims made therein," a Jhajjar police official said, adding that so far 15 people have been booked in the murder case.

Police named former BJP MLA Naresh Kaushik and others in the FIR registered on Monday. It also mentioned five unnamed accused. The case was registered under various IPC sections, including 302 (murder), and the Arms Act.

In his police complaint, Nafe Singh Rathee's nephew Rakesh said five unidentified killers, who were following them in a car, came out and fired indiscriminately near the Barahi railway crossing.

Haryana Home Minister Anil Vij on Monday said the probe into the killing of the INLD's state unit chief will be handed over to the CBI.

Senior INLD leader Abhay Singh Chautala has accused the BJP-JJP government of failing to provide security to Rathee, despite there being a threat to his life.