Air strikes hit rebel positions near a Turkish military post in northwest Syria on Wednesday, where the Russia-backed army has waged a fierce offensive against rebels, according to activists and a senior Turkish security source.
There were heavy clashes between Syrian government forces and fighters about 500 metres from the Turkish observation post in Sher Maghar village, the Turkish source told Reuters.
"However, the conflict is taking place very close by and it is violent. Syrian forces bombed rebel positions," the source said. The source said Turkish soldiers were not affected.
President Vladimir Putin said on Tuesday that Russia and Turkey had agreed steps to tackle militants in northwest Syria and "normalise" the situation there.
Russian and Turkish forces in northern Syria - allies of opposing sides in the civil war but partners in a ceasefire agreement - have been brought closer than ever to direct contact on the ground as the Syrian government presses its offensive into the last major rebel stronghold.
Putin and Turkish President Tayyip Erdogan held talks in Moscow after Syrian army troops encircled another Turkish military post in the town of Morek earlier this month.
A senior opposition official in touch with the Turkish military said Russian special forces had taken up positions around the besieged Turkish Morek outpost to prevent any possible flare-up in the event the Syrian army attacks.
"The Russian presence around Morek is to defuse tensions between the Syrian regime and the Turks," the official, who requested anonymity, told Reuters.
The Russians would protect the Turkish observation post while preventing the Turkish military from responding to any attack, he added. Turkey has retaliated against previous attacks on some of its 12 posts in Idlib and northern Hama.
Syrian President Bashar al-Assad, backed by Russian air power, has gained ground from insurgents this month in the northwest, the country's last big insurgent stronghold. Talks between Moscow, Assad's key ally, and Ankara, which backs some rebel factions, have not managed to end fighting in Idlib.
Turkey has set up 12 observation posts in northwest Syria since reaching a deal with Moscow and Tehran two years ago. Another deal reached last year creates a buffer zone and a ceasefire in the area.
Local activists who track warplanes in opposition territory said air strikes pounded positions around the Turkish post in Sher Maghar village at the edge of Hama and Idlib provinces.
Photos they shared showed large clouds of grey smoke rising from the rural area.
Another rebel source in the area said a Turkish military team was touring the Aleppo-Latakia highway in a reconnaissance mission as part of preparations for a new observation post.
The deal signed by Turkey and Russia last September called for the reopening of traffic over the strategic M5 and M4 highways, from Aleppo to Hama and Latakia, on the Mediterranean coast, two of Syria's most important pre-war arteries.
Residents said heavy air strikes believed to be Russian and Syrian hit other villages and towns in Idlib. A strike hit a market in the city of Saraqeb causing injuries and extensive damage to a main residential area.