DAMASCUS, April 30 (Xinhua) -- The Syrian and Russian Air Force on Tuesday heavily shelled the rebel positions in the northwestern province of Idlib and nearby Hama Province's countryside amid speculation of an imminent operation against the rebels, a war monitor reported.

The Syrian helicopters dropped 35 barrel bombs on the positions of the rebels in the countryside of Idlib and Hama, said the Syrian Observatory for Human Rights.

The London-based watchdog said the Syrian and Russian warplanes had carried out more than 20 airstrikes since early morning Tuesday.

Earlier in the day, the pro-government al-Watan newspaper reported that the Syrian army has started sending reinforcements to Idlib as part of the preparation for a possible operation against the rebels.

The report said the new development comes as Turkey has failed to live up to its pledges regarding the rebels' situation in Idlib, as de-escalation zones' deal reached between Turkey and Russia last September is falling apart.

The army started sending reinforcements to the countryside of Idlib and nearby Hama after the increase in the attacks by the al-Qaida-linked Nusra Front on military positions in the region.

Turkey and Russia brokered a deal last September to impose a demilitarized zone in Idlib and its surrounding areas. However, violations are still being reported on an almost daily basis.

The extremist groups such as the Hayat Tahrir al-Sham (HTS) refused to withdraw from the zone.

On the contrary, the HTS expanded and controlled the entire Idlib area, which is the last major rebel stronghold in Syria.

The Syrian government has repeatedly said Idlib would inevitably return under the government control and the government's patience has limits.