Syrian President Bashar al-Assad attends an interview with a Greek newspaper in Damascus, in this handout released May 10, 2018. Photo: SANA / Handout via Reuters / File.

A ceasefire in northwest Syria reduced violence in the rebel stronghold, a monitor said, with no air strikes on Friday after a three-months army offensive killed hundreds while yielding no big territorial gains.

Though the combatants exchanged fire and shelling on Friday, the British-based Syrian Observatory for Human Rights said Syrian government and Russian warplanes mounted no air raids.

More than 400 civilians have been killed in the escalation since late April and more than 440,000 uprooted, the United Nations said last week.

The targeted region is part of the last major piece of territory which rebels hold after facing defeat across much of Syria at the hands of President Bashar al-Assad with his allies Russia and Iran.

Syrian state media said the ceasefire would start on Thursday night if militants fulfilled a Russian-Turkish deal which had tried last year to create a demilitarized buffer zone.

The Turkey-backed opposition, which is taking part in Syria talks hosted by Kazakhstan, agreed to the ceasefire and said it must “guarantee the safety of civilians.” It reserved the right to respond to “violations by Assad’s regime and its militias.”

Though Turkey-backed rebel factions also operate in Idlib province in the northwest, the dominant force there is the jihadist Tahrir al-Sham alliance, formerly the Nusra Front.

In a statement on Friday, it said the truce declaration from Damascus proved the failure of “the criminal regime’s military operation against the liberated north.” Tahrir al-Sham did not reject the ceasefire but warned that any attack from the other side would cancel it, vowing to retaliate.

Russia’s RIA news agency cited a Kazakh Foreign Ministry official as saying the agreement does not include jihadists who might not observe it.

Turkey is following the situation after the ceasefire reports, the Foreign Ministry said.

“In every talk we hold with Russia, we tell them the (Syrian) regime needs to stop its attacks … but the situation is apparent,” Turkish Foreign Ministry Spokesman Hami Aksoy said.

Under its deals with Moscow, Ankara has forces stationed on the ground in the Idlib region at a dozen military positions.

A series of truce deals have failed to fully end Idlib fighting and Russian-Turkish attempts have not managed to resolve the eight-year conflict.

Syrian state news agency SANA said militants fired missiles that hit a village in government territory, killing one person and injuring three other civilians on Friday.

In the latest offensive, Assad’s side has been unable to gain much ground from the insurgents. The government says it has been responding to militant attacks.

The fighting has also inflicted a heavy toll on both rebel and government fighters: the Observatory war monitoring group says each side has lost around 1,000 fighters.

The United Nations will investigate attacks on UN-supported facilities and other humanitarian sites, Secretary-General Antonio Guterres said on Thursday, after two-thirds of the Security Council pushed for an inquiry.

Britain, France, the United States, Germany, Belgium, Peru, Poland, Kuwait, the Dominican Republic and Indonesia had delivered a demarche — a formal diplomatic petition — over the lack of an inquiry into attacks on some 14 locations in Syria.