Congress general secretary Priyanka Gandhi Vadra sat on a hunger strike on Monday after being detained in Uttar Pradesh's Sitapur while she was en route to Lakhimpur Kheri, her party said.

Gandhi and other Congress leaders accompanying her, including Deepender Hooda, had reached the Lakhimpur border in the morning but were not allowed to meet the families of the farmers who died in the violence during a protest a day earlier, the party alleged.

"Congress general secretary Priyanka Gandhi has been arrested. She is on hunger strike. Congressmen are protesting. The government will have to bow to our demands. Voice for justice will be raised with more strength," the UP Congress said in a tweet.

In a video released by the party, Gandhi was seen sweeping the floor of a room where she was apparently kept.

Stopping them in such a way is "undemocratic", Congress state president Ajay Kumar Lallu told PTI.

Eight people were killed on Sunday as violence erupted during a farmers' protest, claiming the lives of both farmers and BJP workers ahead of a visit to Lakhimpur by Uttar Pradesh Deputy Chief Minister Keshav Prasad Maurya.

On their way to the violence-hit district, Congress leaders had to take alternative routes to reach the bordering Hargaon area in Sitapur as heavy security was deployed on the main roads.

"We are waiting outside Lakhimpur Kheri. We have been prevented by the police from entering. We have come here to meet the victims of the violence," Congress national secretary Dheeraj Gurjar told PTI over the phone at 4.30 am.

Gandhi's convoy was earlier briefly stopped by Uttar Pradesh Police officials in Lucknow, where the Congress general secretary had arrived on Sunday night, within a few hours of violence being reported during an anti-farm laws protest here.

Mobile internet services have been suspended in parts of Lakhimpur district, where restrictions under CrPC section 144 -- which prohibits assembly of four or more people -- has also been imposed, according to officials.

The UP Police took to Twitter early Monday to describe the incident as "unfortunate" and said eight casualties have been reported so far as per the district administration.

"ADG LO, ACS Agriculture, IG Range & Commissioner are on the spot & situation is under control. Adequate deployment has been done to prevent any untoward incident," it added.