LUCKNOW -- Authorities in the Indian state of Uttar Pradesh have appointed a retired judge to probe the violence that broke out during a farmers' protest.

Eight people, including four farmers, were killed after a car linked to junior home minister Ajay Mishra plowed into protesters.

A new video has shown an SUV crashing into the protesters from behind.

Farmers say the minister's son, Ashish Mishra, was behind the attack. The Mishras deny the charge.

Two workers of the ruling Bharatiya Janata Party (BJP) and the driver were subsequently beaten to death by a mob of protesters. A fourth person, a journalist, also died in the violence.

Farm unions say two protesters died when they were run over and two others who were injured later succumbed in the hospital. They are now demanding the purported video footage be treated as evidence against the minister and the son.

But Ajay Mishra continues to deny the charge - he says that neither he nor his son were in the car when the incident happened. Police have started an investigation against them after farm unions vowed to intensify their protests.

The violence, which took place in Lakhimpur district on Sunday, marks a dramatic escalation in a 10-month-old protest against agriculture reforms that the ruling BJP government passed without any substantive discussion in Parliament last year.

And it sparked national outrage this week, leading the Supreme Court to take notice of the loss of life in the clash.

Farmers of Bharatiya Kisan Union protesting against Lakhimpur Kheri incident, at Ghazipur border protest siteImage source, Getty Images

Ahead of the hearing on Thursday, the Uttar Pradesh government ordered an inquiry, saying the matter was of public importance. It has appointed Pradeep Srivastava, a retired high court judge, as a single member commission to investigate the case.

Meanwhile, leaders from main opposition Congress party, Priyanka and Rahul Gandhi, visited Lakhimpuri Kheri on Wednesday and met the families of the deceased farmers and the journalist.

Opposition leaders had been trying to visit the district since Sunday but the state police in Uttar Pradesh barred them from entering the state, citing a law and order situation. Several politicians, including Ms Gandhi, were even detained on their way.

Tens of thousands of farmers have been sitting on the outskirts of Delhi since November, demanding that the laws must be repealed.

It is one of the longest farmers-led protests India has ever seen, pitting the community against Indian Prime Minister Narendra Modi and his BJP government.