Indian police have arrested 22 people after a mob stormed a prison and lynched a rape suspect in the country's north-east, in an act of vigilante justice condemned by rights groups and political leaders.

Several thousand people in restive Nagaland state attacked the prison to drag out a rape suspect, beat him to death and tied the body to a clock tower on Thursday, forcing authorities to impose a curfew to restore order.

"Twenty-two people have been arrested for rioting and attacking the prison complex," Nagaland's top police officer L.L. Doungel told Reuters.

Police said they were struggling to identify people directly involved in the murder of Syed Farid Khan, 35, who had been accused of raping a 19-year-old Naga tribal woman multiple times.

The chief minister of Assam, Tarun Gogoi, on Saturday branded the incident "barbaric, heinous and inhuman" while Amnesty International urged justice for those responsible.

"Violence against women needs to be tackled with swift and effective responses from the state, not with barbarism by self appointed vigilantes," it said in a statement.

Khan's brother, a sergeant in the Indian army, accused police of falsely implicating his brother in the rape to try to root out non-tribals from Nagaland, which is predominantly Christian.

The largest Naga tribe previously campaigned to evict Bengali-speaking immigrants from their territory.

The woman, who cannot be named for legal reasons, said Khan had given her 5,000 ($A103) rupees after the attack in return for her silence.

"It was only after the incident, he gave me the money to keep silent, so I took the money and gave it to the police station," the woman told the NDTV network.

Jamir said the woman's initial medical report "confirmed rape and other ... injuries on her body".

Khan's brother linked the murder to ethnic tensions within Nagaland, whose indigenous groups have for decades accused a growing number of Muslim migrants from Bangladesh of illegally grabbing their fertile land.

The family accused police of falsely implicating Khan in the rape to try to root out Muslims from Nagaland.

The lynching also followed an outpouring of anger in India over violence against women.

Khan's lynching coincided with controversy over a government order to ban the broadcasting of a documentary about the fatal gang-rape in December 2012 of a young student in New Delhi that caused shock within India and around the world.

Muslims in Nagaland and the neighbouring state of Assam protested against the lynching on Saturday and authorities put a freeze on internet and SMS phone messaging services after videos of the attack surfaced.

AFP/Reuters