Two men were arrested on Thursday and Union minister Ajay Mishra's son asked to appear before police in connection with the Lakhimpur Kheri violence that killed eight people.

Ashish Mishra, the son of Union Minister of State for Home, has been asked to come to the police lines at 10am Friday, a notice said.

The Lakhimpur police late on Thursday evening pasted the notice at the Union minister’s residence. The notice, issued under Section 160 of the criminal procedure code that relates to summons to witnesses, said Ashish Mishra must appear in person and present evidences that he is aware of the incident.

“If Ashish Mishra does not abide by the summons, legal procedure will be adopted,” said Lucknow range Inspector General (IG) of police Laxmi Singh.

Two empty cartridges were found at the site of the violence near Tikonia village, police said.

They identified the arrested men as Luvkush of Banbirpur village and Ashish Pandey of Nighasan tehsil, two of the seven people mentioned in an FIR lodged by police.

They were earlier being questioned by police.

Four of the eight people who died on Sunday were farmers, allegedly knocked down by a vehicle carrying BJP workers. Angry farmers then allegedly lynched some people in the vehicles.

The other dead included two BJP workers and their driver.

Farmers claimed that Ashish Mishra was in one of the vehicles, an allegation denied by him and his father who say they can produce evidence to prove he was at an event at that time.

Police said they have formed a nine-member team headed by Deputy Inspector General (Headquarters) Upendra Agarwal to investigate into the FIR lodged against the minister's son and the others.

The arrests came on a day when the Supreme Court termed the Lakhimpur Kheri incident "unfortunate" and sought a status report by Friday from the Uttar Pradesh police.

The court specifically asked the UP Police to specify whether the accused named in the FIR have been arrested. Within hours, the UP Police announced the arrests.

A notice has been pasted at the Union minister's house in Lakhimpur city under section 160 of the CrPC, seeking the presence of his son at the police lines in Lakhimpur to present any oral, written or digital evidence.

According to police, the investigations so far had named an accused and mentioned six unnamed accused.

Three of them had died at the spot. Out of the remaining four, two were arrested on Thursday, a police statement said.

A forensic team went to the site on Wednesday and found two empty .315 bore cartridges. "In the light of this, the incident site was meticulously probed by a metal detector today," the statement said.

During the day, Inspector General (Lucknow) Laxmi Singh and Additional Director General of Police (Lucknow zone) S N Sabat visited the police lines where the two were being quizzed.

Raman Kashyap, a journalist working for a private TV channel, was among the eight people who died on Sunday.

Three people are alleged to have been lynched after an SUV ran into a group of farmers during a protest over a visit by UP Deputy Chief Minister Keshav Prasad Maurya. IG Laxmi Singh said the role of these three was not clear earlier, but "things are becoming clear now".

She refused to divulge anything more.

Asked if the three people who died were the instigators of the violence, the ADG Sabot said events unfolded only after the "accident".

Anyone behind the steering wheel has complete control over the vehicle and is 100 per cent responsible for it, he said.

He suggested that other people in the vehicle could have a reason to instigate or abet whatever happened.