Syrian forces entered parts of a strategic rebel-held town on Monday as Turkey said it would keep hitting President Bashar al-Assad's troops after ramping up operations in its biggest intervention yet into the Syrian civil war.

Turkey and Russia - which have come closer than ever to direct confrontation in Syria in recent days - traded threats over air space after Turkish forces shot down two Syrian government warplanes and struck a military airport.

One million people have been displaced in Syria's Idlib region since December near Turkey's southern border, causing what the United Nations says may be the worst humanitarian crisis in nine years of war.

Turkish President Recep Tayyip Erdogan said he hopes to reach a deal on a ceasefire in Syria's northwest when he meets his Russian counterpart Vladimir Putin later in the week.

"I will go to Moscow on Thursday to discuss the developments in Syria," Erdogan told members of his party in the capital, Ankara.

"I hope that he [Putin] will take the necessary measures there, such as a ceasefire, and that we will find a solution to this affair," Erdogan said in the televised speech on Monday.

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Key town changes hands

A Syrian state television correspondent in Saraqeb said the army was combing the town after the retreat of Turkey-backed rebels. Rebel sources said clashes were continuing in western parts of the town. The Syrian Observatory for Human Rights monitor group said rebels were trying to regain control.

Saraqeb has already changed hands twice in less than a month, reflecting its importance as a gateway to the government-controlled northern city of Aleppo and to rebel-held Idlib city to the west.

Rebels said Turkish drones had been striking Syrian army positions on the Saraqeb frontline, hitting at least two rocket launchers.

Turkey, which has backed rebels fighting al-Assad for much of Syria's nine-year civil war, stepped up its intervention in response to the killing of 34 Turkish soldiers in Idlib last week, the deadliest strike against the Turkish army in decades.

Turkey, which backs certain groups in the last rebel-held stronghold of Idlib, has sent thousands of troops into the province but faces a difficult situation with Moscow backing al-Assad's forces with air power.

"We do not aim to face-off with Russia. Our only aim is to stop the Syrian regime's massacres, radical groups, the displacement of civilians," Turkish Defence Minister Hulusi Akar said on Sunday.

Turkish forces had so far destroyed eight helicopters, scores of tanks, and five air defence systems, Akar said on Monday.

Russia, for its part, said it could not guarantee the safety of Turkish aircraft over Syria, and Damascus said it was closing Syrian air space over the Idlib region.

Also on Monday, the Kremlin said cooperation with Turkey on Syria is a top priority, confirming the meeting between Erdogan and Putin scheduled for March 5.

"Russia attaches "great importance to cooperation with our Turkish partners," Kremlin spokesman Dmitry Peskov said.

Earlier, TASS news agency quoted Putin as saying his country does not plan to go to war with anyone, but wants to dissuade other countries from engaging in conflict with Moscow.

Refugee crisis

Despite backing opposing sides in Syria's war, Turkey and Russia have coordinated closely in the past. In 2018, they reached a deal that led to Ankara establishing 12 military observation posts in Idlib, home to more than three million people, to prevent a Syrian government offensive.

Last month, Erdogan had repeatedly warned that Turkey would push the Syrian government forces away from its military observation posts in Idlib.

The confrontation between Syria and NATO-member Turkey has prompted worries over a wider conflict and a refugee crisis in Europe similar to 2015, when more than a million people fled to Europe in what became the continent's worst refugee crisis since World War II.

Turkey already hosts more than 3.6 million Syrian refugees and says it cannot absorb any more.

Refugee numbers have already surged along the European frontier after Erdogan, seeking to pressure the EU over Syria, said last week the country had "opened the doors" to Europe.

"The [EU] should keep its promises," Erdogan said, referring to a 2016 deal with Brussels to stop the flow of refugees in exchange for billions of euros in financial aid.

Greece said on Sunday it has blocked nearly 10,000 Syrian refugees at its border with Turkey.

Some 13,000 refugees have amassed at the Turkey-Greece border, including families with young children who spent the night in the cold, the International Organization for Migration said.