DAMASCUS, Aug. 1 (Xinhua) -- The Syrian Army said a cease-fire will be implemented in the northwestern Idlib province, the last major rebel stronghold in Syria, starting Thursday evening, according to the state TV.

The state TV cited a military source in the Syrian Army as saying that the cease-fire is based on the de-escalation zones' deal that was reached between Russia and Turkey and approved by the Syrian government last year.

The military source said the "terrorist groups" should retreat 20 km inside Idlib and must hand over their heavy and medium weapons for the cease-fire to take hold and continue.

The situation in Idlib has been escalating since April, as a Russian and Turkish-backed de-escalation zones' deal failed to materialize.

The Hayat Tahrir al-ShamN (HTS), the umbrella group of the al-Qaida-linked Nusra Front, has been engaged in battles with the Syrian Army in Idlib countryside and the adjacent northern countryside of the central province of Hama.

Idlib has emerged as the main destination and stronghold for the rebels fleeing other parts of Syria through deals or surrender.

Several Turkey-backed rebel groups are located in the province near the Turkish border, but the most powerful group there is the HTS.

For the Syrian army, securing Idlib would almost deal a definite defeat to the over eight-year-long insurgency against the administration of President Bashar al-Assad.

Idlib is also strategically important as it shares a border area with Turkey. It's also close to the coastal province of Latakia, the hometown of Assad which contains a Russia-run air base repeatedly targeted by rebel drones launched from Idlib.

The capital city of Idlib also lies close to the international road linking the capital Damascus with Aleppo in northern Syria.

Around 3 million people are living in Idlib, including those evacuated from many other areas during the surrenders of the rebels.