All federal prisons in the US have been placed on lockdown after a gang fight left two inmates dead at a facility in Texas.
Two other prisoners were seriously hurt in the violence at the high security Beaumont facility on Monday, the Federal Bureau of Prisons (BOP) said.
The bureau said it was responding with “an abundance of caution”, adding that the lockdown was a temporary measure.
It is rare for such a measure to apply to the entire federal prison system.
Most of America’s prisoners are held in facilities run by the individual state as opposed to the federal government.
The BOP has 134 facilities housing more than 150,000 inmates around the US, according to the latest information on its website.
When prisons are placed on lockdown, it typically involves inmates being confined to their cells with restrictions placed on visitor access.
In a statement, the bureau said that for “safety and security reasons” it would not provide further details on its decision, adding only that it believed the measure would be “short-lived”.
The violence at the Beaumont facility in Texas, which has a prison population of 1,372, reportedly involved members of the MS-13 street gang – a brutal group established in Los Angeles which has roots in El Salvador.
The fight raised concerns of retaliatory violence that threatened to spread to other prisons, the Associated Press reports, citing sources briefed on the bureau’s decision.
The two inmates who died were named as Guillermo Riojas, a 54-year-old who had been sentenced for violent crimes using a firearm, and Andrew Pineda, 34, who was said to be a member of a gang known as the Mexican Mafia.
No staff members at Beaumont were injured during Monday’s fight, the BOP said.
The Mexican Mafia is believed to have up to 300 members in the prison system. According to the FBI, the gang comprises of current and former convicts who hold positions of power within facilities and offer protection and deal in drugs.
The gang MS-13, which was formed by immigrants who had fled El Salvador’s long and brutal civil war, has a reputation for extreme violence.
The FBI estimates that the group has up to 10,000 members in the US, making it one of the largest criminal enterprises in the country.