Families of prisoners at the Lebanese Roumieh prison claim a mysterious virus has been killing detainees, prompting authorities to launch an investigation.

Three prisoners died in recent days, one of which was caused by an illness while the other was due to cardiac arrest, reports said.

The Presidency of the Lebanese Government asked the ministry of interior to conduct an investigation into the matter, Arabi21 reported.

The Prisons Administration said it has not ruled out drug overdose as a cause.

The Secretary-General of the Council of Ministers Judge Mahmoud Makiya reportedly sent a letter to the Minister of Interior Bassam Mawlawi to investigate the matter.

Roumieh is Lebanon’s largest prison and is grossly overcrowded, triggering ongoing and witnessed mounting discontent among inmates.

"Roumieh prison's main problem is overcrowding, as there are 300% of its capacity, which is 1050, and there are 3,592 in it, which is more than three times," Mawlawi said during an earlier visit to the facility, according to the National News Agency.

“We demand a reduction in all penalties, and we are studying the proposal from a legal point of view with the Minister of Justice and with the Presidency of the Government to find a solution to overcrowding," he added.

Videos from inside the prison that regularly circulate on social media show some prisoners threatening a mutiny in the absence of enhanced safety measures.

They want Lebanon's fractious ruling political class to agree to an amnesty that would reduce the population in Roumieh.

Lebanon has been facing one of its worst economic downturn, leaving three-quarters of Lebanese living in poverty.