All the prisons across the country have been put on high alert after some unidentified miscreants issued threats to take away militant prisoners from jails.

Apart from jail authorities, Lalmonirhat Deputy Commissioner Abu Jafor claimed to have received a letter and phone call threatening to blow up the district jail if detained militants are not freed.

"The threats came over phone and in letters," said a letter signed by Inspector General (IG) of Prisons Brig Gen AKM Mustafa Kamal Pasha on Sunday.

The letter directed all the prisons in the country to remain on high alert and issued an 18-point instruction to beef up security there.

The instructions include formation of a striking force consisting of a deputy jailer and keeping a chief jail guard and five jail guards in each prison ready to prevent any possible attack.

The striking force will monitor the movements of all the inmates, especially the militants and others accused of sensitive cases like those of the Border Guard Bangladesh (BGB).

At the entrances of the jails, prisons guards were asked to wear bullet-proof jackets and helmets and use metal detectors to check visitors.

The IG directed them to use armed sentries and ensure the security of weapons and arsenals and monitoring of CCTV footage persistently.