SAN SALVADOR – At least three inmates were murdered and another is missing at the Chalatenango prison in northern El Salvador, officials said.

The three bodies were found Saturday night in different parts of the prison and the missing inmate may also have been murdered, the director of the national bureau of prisons, Nelson Rauda, said.

The killings may be linked to a fight involving members of rival gangs, Rauda said, without disclosing how the men were murdered.

A state of emergency has been declared at the Chalatenango prison for 10 days, with inmates ordered to remain in their cells and all visits cancelled, Rauda said.

Three inmates were murdered in December at the prison in Chalatenango, located about 72 kilometers (45 miles) north of San Salvador.

Prison officials, meanwhile, discovered a tunnel Saturday at the San Francisco Gotera prison in eastern El Salvador that prisoners apparently planned to use for an escape.

El Salvador’s 21 prisons are designed to hold about 8,300 prisoners, but they currently house more than 24,000 inmates, official figures show.