Russia's defence ministry said Syrian regime forces will unilaterally cease-fire in the "de-escalation zone" in Idlib region on Saturday 0300 GMT.
Syrian residents and army defectors reported an escalation in the Assad regime and Russia's military operations in northwest Syria, just as Moscow announced the regime would cease fire in the coming hours.
The Russia-backed Syrian regime stepped up an offensive against the last big stronghold of Syrian opposition and rebels in the northwest, mounting more air raids and deploying ground reinforcements including Iranian-backed militias, army defectors and residents said on Friday.
The Russian-led alliance was pushing into densely-populated parts of Idlib province in the northwest where millions of people who fled fighting elsewhere in Syria have taken refuge.
Jets flying at high altitude dropped bombs on the outskirts of Idlib city, the heavily-populated provincial capital.
The aircraft were believed to be Russian, according to activists who track the warplanes' activities.
The northwest offensive has prompted UN warnings of a new humanitarian crisis amid the gains by Damascus and its partner Moscow, which has helped regime leader Bashar al Assad turn the tide in the eight-year-old conflict since intervening in 2015.
Moving deeper into territory along the Turkish border, the advance took the town of Tamaneh after earlier capturing Khwain, Zarzoor and Tamanah farms, the defectors and residents said.
They were the first gains since the alliance seized a main rebel pocket in nearby Hama province last week.
The offensive has been reinforced by elite regime units and Iranian-backed militias, the defectors and residents said.
"There are daily reinforcements coming from the Iranian militias, elite Republican Guards units and Fourth Armoured Division," Colonel Mustafa Bakour, a commander in Jaish al Izza rebel group, told Reuters.
TRT World 's Oubai Shahbandar brings more from the Turkey-Syria border.
Ceasefire in Idlib
Russia announced the Syrian regime would cease fire in the northwestern province of Idlib from Saturday morning 0300 GMT.
An agreement was reached on "a unilateral ceasefire by Syrian regime forces in the Idlib de-escalation zone, from 6:00 am on August 31," the Russian Reconciliation Centre for Syria said in a statement.
The statement said the ceasefire aimed "to stabilise the situation" in Idlib and urged anti-regime fighters to "abandon armed provocations and join the peace process."
Turkey, Russia and Iran agreed in 2017 to make Idlib a de-escalation zone to reduce fighting, although the terms were never made public and the deal did not include jihadist groups.
Foreign Minister Sergey Lavrov said earlier this month that Russia had military personnel on the ground in Idlib province.
In recent weeks, Moscow sent more special forces that helped break months of stalemate on frontlines where rebels had been holding the army back, Western intelligence sources have said.
After months of intense bombardment, regime forces launched a ground offensive against Idlib earlier this month.
The UN says that over 550 civilians have been killed and over 400,000 people displaced from northern Hama and southern Idlib provinces since the offensive on Idlib began in late April. Other groups estimate the death toll has crossed 800 since April.
Syria's war has killed more than 500,000 people and displaced millions since it started in 2011.