Turkey urged Russia on Tuesday to rein in Syrian government forces in the northwestern province of Idlib, a day after eight Turkish personnel were killed in an attack Ankara blamed on Russian-backed Syrian troops.
The two countries back opposing sides in the war, with Russia supporting President Bashar al-Assad and Turkey backing rebels who once aimed to topple him.
They have worked together to reduce fighting in Idlib, but a major Syrian government offensive in the region has rattled Ankara, which fears millions of displaced people could be driven towards Turkey, which already hosts 3.6 million refugees.
While Turkey has urged Russia to restrain Syrian forces from launching further attacks, Moscow says it is concerned about attacks by militants who control Idlib, the last remaining major rebel stronghold after nearly nine years of war.
On Monday, Turkey bombarded dozens of targets around Idlib in response to the deadly attacks on its troops.
"I told my counterpart Sergei Lavrov that the regime was carrying out provocative attacks on our observations posts around Idlib, that we will retaliate if they continue this, and that they need to stop the regime as soon as possible," Cavusoglu told reporters.
"We also don't accept the excuse of 'we cannot fully control the regime' here," he said, adding that agreements with Russia regarding Idlib must be revived.
Turkey is building housing for displaced people near the Turkish border, where President Tayyip Erdogan said on Monday nearly 1 million people were heading.
United Nations regional spokesman David Swanson said 520,000 people had been displaced since the beginning of December. He said an additional 280,000 people could be displaced from urban centers near the two main highways in the region.
Konstantin Kosachev, a senior Russian lawmaker, said Moscow was very concerned about the situation in Idlib, calling it a "serious test of the strength of the existing Russian-Turkish agreements" in both Idlib and in northeast Syria, where the two countries have been carrying out joint patrols.
A Turkish security official said clashes between Turkish and Syrian forces continued intermittently around Saraqeb, a town 15 km (9 miles) east of Idlib city.
He said Turkey had no plans to withdraw from 12 observation posts it established in the area as part of a 2017 agreement with Russia and Iran, even though some posts are now surrounded by Syrian government forces.
"There is information that some observation posts have been besieged by the regime, but the (supply of) new weapons, equipment and military support towards Idlib is continuing," the official said, speaking on condition of anonymity.
Fighting in Idlib has continued in recent years despite several ceasefire efforts, including as recently as last month, and renewed bombardments by Russia-backed government forces have displaced hundreds of thousands of civilians.