Pakistan's prison system is under scrutiny after a series of jailbreaks by Taliban and al-Qaeda-linked fighters freed hundreds of prisoners.
There are fears that the main prison at the country's biggest city, Karachi, is next in line, after fighters threatened to attack the facility.
Pakistani authorities have stepped up security by installing mobile phone jammers and deploying more guards, but officers say the task of defending prisons remains difficult.
Al Jazeera's Imtiaz Tyab reports from Karachi.
Source: Al Jazeera