Union minister Ajay Mishra's son is among those booked in connection with the violence during a farmers' protest in Lakhimpur Kheri, officials said on Monday as multiple opposition leaders tried to make their way to the Uttar Pradesh district through the night but were prevented from doing so.

Two FIRs were registered a day after clashes claimed the lives of eight people, including four farmers allegedly run over and four people in a convoy of BJP workers who were lynched, the incident propelling Lakhimpur Kheri as a new flashpoint in poll-bound Uttar Pradesh.

Punjab Congress leader Navjot Singh Sidhu was detained in Chandigarh today for protesting against UP violence, according to NDTV.com.

The Uttar Pradesh government will give Rs 45 lakh each and a government job at the local level to the family members of the four farmers killed in Lakhimpur, said Additional Chief Secretary, Home, Awanish Kumar Awasthi.

As tempers ran high and the opposition trained its guns on the BJP-led state government, Congress general secretary Priyanka Gandhi Vadra, SP president Akhilesh Yadav, Chhattisgarh Chief Minister Bhupesh Baghel, BSP's S C Mishra and AAP's Sanjay Singh were among those prevented by police from going to the trouble spot, about 80 km from the district headquarters and 225 km from Lucknow.

"FIR has been lodged against several persons, including Minister of State for Home, Ajay Mishra's son Ashish Mishra," Awasthi told PTI in Lucknow.

Additional Director General, Law and Order, Prashant Kumar, who was in Lakhimpur Kheri, added that two FIRs from both sides had been registered in the incident, the bloodiest yet in the prolonged farmers' protest against the Centre's new agri laws that began last year. The details were not known immediately.

Detailed information is not available as yet as the internet is not working here, he told PTI in the morning.

The Samyukta Kisan Morcha (SKM), an umbrella body of farm unions, wrote to President Ram Nath Kovind, demanding that the minister be sacked and a murder case filed against his son. It also demanded an investigation by an SIT under the supervision of the Supreme Court.

Sources in Lakhimpur Kheri said the FIR against Ashish Mishra and a few others was registered by a man called Jagjit Singh, probably a farmer. The farmers were protesting the visit of Deputy Chief Minister Keshav Prasad Maurya. They also set on fire two SUVs.

Bharatiya Kisan Union leader Rakesh Tikait, who managed to reach Lakhimpur Kheri in the early hours of Monday, submitted a memorandum to the district administration to demand Mishra's sacking and compensation of Rs 1 crore as well as a government job for the family members of farmers who were killed.

"After our demands are met... only then we will cremate the (farmers)," he said as tension spiralled in the area.

During a press conference, some farmers alleged that Ashish Mishra also opened fire on farmers. Ajay Mishra has said he and his son were not present at the spot as alleged and he has photo and video evidence to prove it.

Sources in Lakhimpur said nobody, including journalists, is allowed to visit Tikonia where the violence took place. Policemen were deployed at all entry points of the district to stop the entry of outsiders.

As Chief Minister Yogi Adityanath went into a huddle with senior officials to view the law and order situation, police stopped prominent leaders from entering the district.

With the incident coming ahead of elections in the politically vital state, opposition parties sharpened their attack on the BJP government.

Priyanka Gandhi had arrived in Lucknow on Sunday but was detained in Sitapur around 5 am, Congress state President Ajay Kumar Lallu told PTI.

As videos did the rounds of a furious Priyanka Gandhi lashing out at police personnel for misbehaving with her and her colleagues, Lallu alleged that policemen pushed Congress leaders.

"The BJP government is doing the politics of crushing the farmers and finishing them," she said on Twitter.

Saying that farmers will win this fight for justice, former Congress president Rahul Gandhi added in a tweet in Hindi, "Priyanka, I know that you will not retreat. They fear your courage. We will ensure that the country's 'annadatas' win this non-violent fight for justice."

Congress also staged protests in the national capital.

Priyanka Gandhi put out a video message alleging that this country belongs to the farmers and not to the BJP. She said she was going to Lakhimpur to share the pain of the farmers injured in the violent clashes and it was no crime.

In Lucknow, Akhilesh Yadav took up the theme. He was stopped outside his Lucknow home in the morning after which he sat on dharna' with his party leaders.

"To suppress voices, vehicles are being run over by those who raise voices. We want the arrest of the Minister and his son in the Lakhimpur incident, he told reporters.

A police jeep parked in front of the Gautam Palli police station near his dharna was also set on fire allegedly by SP workers.

BSP general secretary S C Mishra was also detained at his home in Lucknow on Sunday night on the plea of maintenance of law and order.

BSP supremo Mayawati demanded a judicial probe into the Lakhimpur incident.

AAP's Sanjay Singh and Shivpal Yadav were also barred from going to Lakhimpur Kheri and so were Congress leaders Salman Kurshid and Pramod Tiwari.

Besides, the Uttar Pradesh government requested airport authorities in Lucknow to not allow Baghel and his Punjab counterpart Chandrajit Singh Channi, who had announced plans to visit Lakhimpur Kheri.

A furious Baghel, who has been made senior observer by the Congress for the UP Assembly elections, told reporters in Raipur, my plane is ready, but the UP government has denied landing permission (at Lucknow airport)."

When Section 144 (of CrPC) is in force in Lakhimpur, why should landing at Lucknow not be allowed, he asked.

BJP's Pilibhit MP Varun Gandhi also took up the issue in a big way. He wrote to the chief minister to demand a CBI probe under the supervision of the High Court.

Varun Gandhi, whose Lok Sabha constituency is close to Lakhimpur Kheri, sought Rs 1 crore as compensation to the families of each of the farmers and said those involved in their death should be booked for murder.

Underlining that the "agitating farmer brothers are our own citizens", the three-time BJP MP from Uttar Pradesh said, "We should deal with them with great restraint and patience. In any case, we should treat our farmers with sensitivity and only in Gandhian and democratic way within the ambit of law."

Uttar Pradesh government spokesperson and cabinet minister Sidharth Nath Singh termed the opposition move to go to Lakhimpur a political stunt aimed at vitiating the peace.