LUCKNOW -- Security has been tightened in a northern Indian town after eight people, including four protesting farmers, died on Sunday.

Violence broke out in India's Uttar Pradesh state on Sunday after a car linked to a federal minister ran over two farmers taking part in a protest against controversial farm laws, local newspapers reported.

In subsequent clashes, three members of India's ruling Bharatiya Janata Party, a driver and two other farmers were killed, according to party and police officials.

The violence broke out in the Lakhimpur Kheri district, about 130 kilometers (81 miles) north of the state's capital Lucknow.

Uttar Pradesh Chief Minister Yogi Adityanath's office said an investigation was underway.

The incident sparked further protests and road blockades in some parts of the state and prompted an outcry on social media from opposition leaders.

Farmers alleged the car was owned by the son of Ajay Mishra, who serves as India's junior home minister. The two farmers who were hit were killed, they said.

Mishra said his son was not present at the incident, but that a car driven by "our driver" had lost control and hit the farmers after "miscreants" pelted stones at the car and attacked it with sticks and sword.

"If my son would've been there, he wouldn't have come out alive," he told Reuters TV partner ANI.

Photos and videos on social media showed vehicles set on fire as people lay covered in blood.

Opposition leaders have been stopped from visiting the families of the victims as the situation remains tense.

Several prominent farm leaders, including Rakesh Tikait, reached the violence-hit district on Monday morning. Tikait told the media that farmers will hold discussions with the villagers before deciding their future course of action.

Akhilesh Yadav, former Uttar Pradesh chief minister, told the BBC that the police had stopped him from leaving his residence.

"The prime minister says ours is a vibrant democracy. But stopping opposition leaders from going to Lakhimpur doesn't really strengthen our democracy. Farmers, who are the backbone of our economy, cannot be treated like this," he said.

"Their fears are legitimate about private players hurting their income and they should be heard. We need to strengthen our farming systems and not weaken them."

Senior Congress party leader Priyanka Gandhi was also detained on Monday while she was on her way to meet the families of farmers who died in the violence.

Violence in Lakhimpur Kheri marks a dramatic escalation in a 10-month-old protest against agriculture reforms that farmers say will benefit private players at their expense.

Tens of thousands of them have been striking 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 Bharatiya Janata Party-led (BJP) government. -- Agencies