Two Indian senior opposition leaders -- Priyanka Gandhi Vadra of Congress and Bahujan Samajwadi Party supremo Mayawati -- today demanded probe into the death of a TV journalist who recently reported on the "liquor mafia" in Uttar Pradesh state.

Priyanka wrote a letter to Uttar Pradesh's BJP Chief Minister Yogi Adityanath demanding a Central Bureau of Investigation probe into the "mysterious" death of Sulabh Srivastava on Sunday, reports our New Delhi correspondent.

The Congress General Secretary also demanded that action be taken against the "nexus of liquor mafia and the administration" which she said had taken root across the state. 

Srivastava died under "mysterious circumstances" on the night of June 13 in Pratapgarh district while he was returning home after news coverage, Priyanka Gandhi wrote in the letter.

On the other hand, Mayawati demanded "a swift, impartial and credible probe into the death of the journalist."

The Uttar Pradesh Police on Monday registered a case of murder after 42-year-old Srivastava died in what appeared to be a road accident.

In a tweet in Hindi, Mayawati said, "The terror of the liquor mafia is known to all. The gruesome murder of a TV news channel reporter for exposing their black deeds is extremely saddening."

"The government must ensure stringent punishment to the guilty by carrying out a swift, impartial and credible probe," she said.

Samajwadi Party President Akhilesh Yadav had on Monday demanded a high-level inquiry into the death while West Bengal Chief Minister Mamata Banerjee expressed shock over the incident saying "we are unable to save lives who are working tirelessly towards unfolding the truth".

Superintendent of Police Akash Tomar had told reporters that "Sulabh Srivastava had gone for news coverage to the Kotwali Lalganj area on Sunday and was returning home late in the night. He was found seriously injured near a brick kiln and was taken to the district hospital where doctors said he was 'brought dead'."

His motorcycle had rammed into a pole near the brick kiln under the Kotwali police station area in Pratapgarh district, police said.

The journalist's wife, Renuka Srivastava, in her police complaint, said her husband was being threatened for doing a story against the liquor mafia and the Prayagraj Additional Director General of Police was informed about it in writing but no effective action was taken.

"Because of this, unknown mafia elements murdered my husband on Sunday night while he was returning from Lalganj after news coverage," she had alleged in her complaint.