At least 60,000 people have died in Syrian government jails during the past five years of war, a new report has found.

The Syrian Observatory for Human Rights (SOHR) report said tens of thousands of people had been killed by the regime of Bashar al Assad, either as a direct result of torture or denial of food and medicine.

SOHR, a British-based monitoring group, said it had arrived at the number by adding up death tolls provided by sources in several Syrian jails and security agencies.

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UN investigators said in February detainees held by the Syrian government were being killed on a massive scale.

The report came as rebel groups vowed to no longer abide by a “cessation of hostilities” and set a 48-hour deadline for the US and Russian sponsors in Syria’s conflict to halt a regime offensive in the Damascus region.

“We are giving the sponsors of the ceasefire 48 hours to rescue what remains of the accord and to force the criminal regime of [President] Assad and his allies to completely and immediately halt their brutal offensive against Daraya and Eastern Ghouta,” 29 rebel groups said in a joint statement.

“In view of the regime’s offensive against all the liberated regions, in particular Daraya … we consider the ceasefire accord to have totally collapsed.

“Rebel groups will take all possible measures and respond with all means to defend our people and on all fronts until the regime totally halts its offensives against all liberated regions, especially Daraya, and pulls back to its pre-May 14 positions.”

Syria recaptures towns in Damascus region

Syria’s army, backed by Lebanon’s Shiite militia Hezbollah, recaptured the town of Deir al-Assafir and nine nearby villages in the Damascus region on Thursday, taking advantage of clashes in the Eastern Ghouta area between rival rebel groups Jaish al-Islam and Faylaq al-Rahman – which were among those listed on the joint statement.

Hundreds of families fled the area, which Islamist rebels had controlled since 2012.

The town of Daraya, also near the capital, was one of the first to erupt in demonstrations against the government in 2011. It has been under a strict regime siege since late 2012.

The rebel groups urged the international community and friendly nations “to act to save Daraya from genocide”.

Anti-regime group the Local Coordinating Committees said clashes were taking place in suburbs of Daraya on Sunday, and the pro-regime Al-Masdar website said the army “is preparing a major operation” to capture it within the next few days.

The political opposition coalition said in a statement it backed the decisions of rebel groups and “supports their demands”.

– ABC