The union home ministry has sought a report about the incident from the Manipur government since Saudi Arabia is seeking information on the killings of its two citizens, the sources said.
The incident occurred at about one a.m. on Saturday.
Sources said two Saudi Arabians identified as Sushak Ahmed and Abdul Salam, in their mid 40s, allegedly killed a local man, Thangmilien Zou of Churachandpur district of Manipur, shortly after midnight.
Zou's skull was smashed apparently with both blunt and sharp weapons, they said. It is yet to be established how the killers managed to smuggle the weapons into the prison.
On learning that Zou had been killed other inmates beat the two foreigners to death, sources said.
Though the mayhem continued for more than an hour, there was no intervention from the prison staff and security personnel, they said.
The two Saudi Arabians had been arrested by police at Moreh, the border town, for entering Manipur without valid travel documents in 2013. They have been in judicial custody facing trial.
Zou had been arrested in 2010 in connection with a murder case.
The bodies were taken to J.N. Institute of Medical Sciences hospital for post mortem.
While the body of Zou will be handed over to his family members, India is in touch with Saudi Arabia about the bodies of the two Saudi Arabians.
The police station at Heingang has registered a case.
Though there had been group clashes among inmates and even a revolt against prison authorities in the past, in which several persons including the IGP (Prisons) were injured, this is for the first that inmates have been killed.
Manipur Home Minister Gaikhangam refused to comment on Saturday's incident. Security measures have been beefed up in the central jail to ensure that there is no further violence.
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