Relations between Russia and Turkey continued to sour as the two countries edged closer to open confrontation over northwest Syria while their top officials struggled to defuse tensions.

Meanwhile inside embattled northwest Syria, Turkish-backed rebel fighters and Assad regime troops fought ferociously for towns and villages in Syria's northwest. A Syrian monitoring group described a Turkish drone strike which killed 19 regime troops in a convoy on Monday.

An activist described improving humanitarian conditions as the regime’s forces find themselves on the defensive in the face of a Turkish artillery and air onslaught.

“Now the situation has become better than before,” said Mustafa Dahnon, a journalist reached by telephone in the city of Idlib, the most heavily populated urban centre in the contested opposition-controlled province.

“Because the military factions managed to regain control of villages, towns and cities,” he told The Independent. “In the past, the regime was very close to the city Idlib. Now they have been pushed back.”

The escalating violence in Syria has prompted the Turkish President Recep Tayyip Erdogan and Russian President Vladmir Putin to hold a hastily arranged meeting in Moscow on Thursday, the Kremlin announced Monday. Russian and Turkish troops also conducted a joint patrol in northern Syria on Monday in an attempt to restore fraying ties.

The fast-moving developments came following the killing of at least 33 Turkish soldiers in a Syrian regime airstrike in Idlib province on Thursday. The attack prompted Ankara to dramatically escalate attacks on military forces loyal to President Bashar al-Assad and open its borders at Bulgaria and Greece to refugees yearning to head towards the west.

On Sunday, Turkey claimed it downed two Russian-made Syrian regime fighter jets over the country’s opposition-controlled northwest and rendered useless a regime airbase near the town of Nayrab, according to Turkish media outlets. Damascus claimed it shot down a Turkish drone near the town of Saraqeb.

Neither claim could be independently verified.

Hours later Damascus announced a no-fly zone over northern Syria, according to the official Sana news agency, a restriction it would be unable to enforce without Russia, its primary patron and military backer.

Turkey’s defence minister Halusi Akar on Sunday announced the launch of Operation Spring Shield, aimed at pushing back Assad’s forces from Turkey’s positions in Idlib.

“We do not aim to have a face-off with Russia,” Mr Akar said. “Our aim is for the Syrian regime to stop massacres and to prevent radicalisation, migration.”

Mr Akar said the Turkish offensive would entail targeting Assad regime assets that posed a threat to Turkish interests in northeast Syria.

Turkey has been hammering Syrian regime positions with artillery and airstrikes for days, claiming to have “neutralised” several drones and helicopters, as well as dozens of tanks, howitzers, several air defence systems and 2,212 regime soldiers, according to Halusi.

Meanwhile Turkey detained three journalists working for the Kremlin-operated Sputnik website after it published a piece questioning the Turkish annexation of a part of Syria some eight decades ago. The journalists were later released under pressure from Moscow.

Turkey has long been the primary patron of Syrian opponents to the Assad regime, but finds itself backed into the corner as his forces, backed by Russian air power and Iranian ground forces, have reconquered much of the country.

Northwestern Idlib province remains the final opposition stronghold, and for months both the Assad regime and Russian forces have been pummelling it and its estimated 2 million civilians with airstrikes and artillery, creating a humanitarian disaster and a potential domestic political nightmare for Mr Erdogan in a Turkey increasingly hostile to Syrians.

Mr Erdogan and Mr Putin forged a partnership over Syria over the last several years, attempting to find a resolution to a nine-year conflict that began with Mr Assad’s violent suppression of peaceful protesters and mushroomed into an all-out civil war.

A collapse in the detente between Moscow and Ankara could mean direct armed conflict between a Nato member and Russia, potentially entangling the rest of the alliance. It could also spell more misery for millions of Syrians penned up in the country’s northwest hoping to get to western Europe.

Mr Erdogan’s government has claimed it allowed 117,000 migrants and refugees to get across the border towards Greece and Bulgaria as a way of putting pressure on the European Union to address Syria and to deflect domestic attention away from the losses the conflict has entailed.

Greek and Bulgarian authorities are reporting far fewer numbers attempting to cross and insist very few if any are successful in traversing the heavily guarded frontiers.