The leaders of Russia and Turkey said Tuesday they shared deep concerns over fighting in northwestern Syria, with Ankara warning it would take the steps necessary to protect its troops there.
After meeting for talks near Moscow, Russian President Vladimir Putin and Turkey's Recep Tayyip Erdogan said they hoped to work together to ease tensions in Idlib province.
Russian-backed government forces launched a ground offensive this month against Idlib, one of the last major areas of Syria outside government hands.
The fighting is threatening to increase tensions between Russia and Iran, who back President Bashar al-Assad's regime, and Turkey which supports some rebel groups.
"The situation in the Idlib de-escalation zone is of serious concern to us and our Turkish partners," Putin said at a press conference with Erdogan carried on Russian state television.
He said Turkey had "legitimate interests" to protect on its southern borders and supported the creation of a security zone in the area.
Putin said he and Erdogan had agreed "additional joint steps" to "normalise" the situation in Idlib, but did not provide details.
Moscow and Ankara last year struck a deal to create a "de-escalation" buffer zone around Idlib to avert a full-scale regime assault.
But Assad's forces have been bombarding the province for months and on August 8 launched a ground offensive.
Turkey established 12 military observation posts in Idlib under the buffer zone deal and one of them has been encircled by Syrian government forces.
- 'Our troops are in danger' -
"The situation (in Idlib) has become so complicated that at this moment our troops are in danger," Erdogan said.
"We do not want this to continue. All necessary steps will be taken here as needed."
Tuesday's talks between Putin and Erdogan came ahead of a summit on Syria that will see the two leaders joined by Iran's President Hassan Rouhani in Ankara on September 16.
Erdogan said the September meeting "should contribute to peace in the region".
Both leaders said they supported Syria's territorial integrity, but Putin emphasised the need to keep fighting jihadist forces in Idlib.
"Terrorists continue shelling the positions of Syrian government forces, trying to attack Russian military installations," Putin said.
"The de-escalation zone must not serve as a refuge for militants, let alone a bridgehead for new attacks."
Idlib is dominated by jihadist group Hayat Tahrir al-Sham, the former Al-Qaeda affiliate in Syria.
Recent fighting has been fierce in the province, the last major front in a war that has killed more than 370,000 people and displaced millions since 2011.
On Tuesday, clashes between anti-government fighters and regime forces in northwestern Syria killed 51 combattants on both sides, according to the Syrian Observatory for Human Rights, a Britain-based war monitor.
Putin and Erdogan met on the sidelines of the MAKS international air show on the outskirts of Moscow -- a showcase for Russia's military and civil aerospace industry.
The two leaders highlighted their increased cooperation, which saw Turkey begin taking delivery in July of Russian S-400 missile systems it ordered in defiance of warnings from Washington.
Turkey's defence ministry said the second stage of deliveries had begun on Tuesday and would last for a month.
Putin said he and Erdogan had discussed further military cooperation, including on Russia's Sukhoi Su-35 fighter jet.
A move by NATO member Turkey to purchase Russian fighters would be sure to further anger Washington.
"We have many opportunities, we demonstrated new weapons systems and new electronic warfare systems," Putin said. "In my opinion there was a lot of interest from our Turkish partners."