Syrian regime forces together with their Russian allies have increased air strikes and shelling in the jihadist-controlled northwestern province since last April.

"We expect Russia to take effective and decisive measures to ensure regime forces end their attacks on the south of Idlib and the (forces) immediately withdraw to the borders agreed as part of Astana Process," Turkish Defence Minister Hulusi Akar said.

"The regime is trying to widen its area of control in Idlib's south in violation of the Astana agreement," Akar added, quoted by state news agency Anadolu.

He said the attacks were also a "risk" to Turkey's 12 military observation posts around the region.

Akar made his comments during a visit to the Turkish border with Syria, joined by top military commanders.

While Moscow backs Syrian President Bashar al-Assad, Ankara has called for his ouster and supports Syrian rebels in the civil war which began with anti-government protests in 2011.

Despite being on opposing sides of the war, Turkey has been working closely with regime backers Russia and Iran to find a political solution to the Syrian civil war.

Their talks have been known as the Astana process which was launched in early 2017, in the Kazakh capital now called Nur-Sultan.

A separate deal agreed by Moscow and Ankara last year aimed to set up a buffer zone around Idlib, and avoid a massive Syrian regime assault on the province.