KARACHI: Pakistani officials said Monday they had thwarted a militant group’s bid to tunnel into Karachi’s main prison and stage a jailbreak that could have freed 100 dangerous militants.

The government paramilitary Rangers raided a house where members of a militant group were trying to tunnel into the nearby Karachi Central Jail, Rangers Col. Tahir Mehmood told a press conference.

Breakouts from Pakistan’s ageing, overcrowded prisons are not uncommon. A raid by heavily armed militants on a jail in the northwest last August freed nearly 250 prisoners, while almost 400 fled in a similar incident in another northwestern prison in 2012.

Mehmood said they had arrested suspects from a banned militant organization but did not name it or say how many were detained.

The Karachi jail holds a large number of high-profile sectarian militant detainees and has repeatedly come under threat in recent years.

Mehmood said that the 45-meter tunnel had been dug from an underground water tank at the house toward a dry well inside the jail boundary, and was just 10 meters short of its target when the Rangers made their raid.

“Nearly 100 dangerous terrorists were present in the cell near the well where the suspects wanted to enter through the tunnel,” he said.

Authorities had fortified the jail by erecting double boundary walls in view of the threats and jammers were also installed around the jail to prevent any bomb attack.