World Bulletin/News Desk

Lebanese forces stormed the country's largest prison on Monday where militants are detained, security sources said, as authorities searched for those behind a double attack at the weekend.

Interior Minister Nohad Machnouk headed to Roumieh prison east of Beirut early on Monday and told Reuters the crackdown came after intelligence showed some of the inmates were connected to the bombings, which killed eight.

"We made sure of their involvement in the bombings... through monitoring their communications," he said, adding that suspects would be moved to a separate section of the prison.

Prisoners torched mattresses to protest the move, the sources said, but there were no injuries. Security sources said the police were searching for "forbidden items" at Building B in Roumieh, where militants are held.

The Nusra Front, some of whose members are being detained in the prison, threatened to retaliate.

Roumieh was originally built to hold about 1,500 inmates, but is now crammed with about 3,700. Roumieh holds many high profile convicts and government officials have previously warned that it is a hotbed for extremism.

Machnouk said that prisoners were able to communicate with militant organisations using mobile phones and the internet-based Skype programme.

Television footage showed police entering and searching prisoners' rooms and smoke rising from the jail.

"I can confirm that Roumieh prison is an operations room for Daesh," he said, using a derogatory name for ISIL, a Sunni militant group that has taken control of parts of Syria and Iraq and is also active in Lebanon.

Militants linked to ISIL and the Nusra Front are holding around two dozen members of the Lebanese security forces who were seized in an assault on the Lebanese border town of Arsal last August.

Four have been killed in detention and the Nusra Front threatened on Monday action against the remaining captives following the prison raid.

"As a result of the deterioration of security in Lebanon, you will hear about surprises regarding the fate of the prisoners with us," the Nusra Front said on its Twitter account.

The group had previously claimed responsibility for Saturday's double suicide attack on a cafe in a predominately Alawite district in Lebanon's second biggest city, Tripoli.

Lebanon has been buffeted by the war in neighbouring Syria, which pits a majority Sunni insurgency against President Bashar al-Assad, an Alawite. Hezbollah, a Lebanese Shi'ite Muslim group, is fighting alongside Assad's troops, further angering many Sunnis in Lebanon.