AMMAN (Reuters) - Syrian rebels said on Saturday the Syrian army and their allies were intensifying attacks on a demilitarised zone in the northwest in an attempt to undermine a Russian-Turkish deal that has averted a major offensive on their last stronghold.

They said the army has stepped up its onslaught with hundreds of mortar and rocket attacks on a string of rebel-held villages and towns in northern Hama, southern Idlib and Latakia that fall within a demilitarized zone agreed last September between Russia and Turkey.

“The regime has targeted all the fronts in the demilitarised zone. We have responded by striking at their military posts that have struck populated villages and towns,” said Captain Naji Abu Huthaifa, a spokesman for the National Liberation Front, an alliance of Turkish-backed rebels.

Russia and Turkey reached a deal in Sochi last September to enforce a demilitarised zone in Idlib and adjacent areas that are the last stronghold of rebels who rose against President Bashar al-Assad in 2011.

Idlib province is also home to an estimated 3 million people, more than half of whom have already been displaced at least once during the war.

The Syrian army and allied militias had wanted to press on to regain the last of the rebel held areas after recapturing southern Syria and ending insurgent control around the capital.

Syrian state media, quoting army sources, blamed rebels for the attacks and accused them of trying to wreck the Russian-Turkish initiative.

Under the deal Turkey had pledged to drive out al Qaeda-inspired jihadists from the zone, but Russian military is increasingly questioning Ankara’s ability to implement it.

The main jihadist group, Tahrir al Sham, has so far not withdrawn heavy weapons, a regional intelligence source said on Saturday.

A suicide attack by the Ansar al Islam militant group on an army checkpoint on Friday had killed at least twenty three soldiers, rebels said.

But despite flareup in violence, the Russian and Syrian airforce have so far not resumed aerial bombing since the deal.

The attacks have also forced hundreds of families that had earlier been encouraged to return to some of the frontline villages in the zone to flee further north near the Turkish border, residents said.