The Idlib region, which sits on the Turkish border, is now the last major stronghold of opposition to the Russia-backed government of President Bashar al-Assad.
But the jihadists of HTS failed to pull back from the zone as agreed and in April government and Russian forces resumed intense bombardment of the region. There was no immediate word on casualties from the airstrike on the Rahma hospital in Tel Mannas, said the Observatory and the Thiqa news agency, an activist collective.
Insurgents in Syria have suffered a series of setbacks over the past three weeks in the face of a stepped-up government offensive in the country's northwest - the last rebel-held territory in Syria.
Other sources from the Syrian opposition said that during the ongoing talks with Russia, Turkey was trying to open a supply route to its observation point in Morek from the M5 highway that passes through Khan Sheikhoun and Tal al-Nimr.
The announcement came a day after government forces captured the key Idlib province town of Khan Sheikhun from jihadists and allied rebels.
Under the deal, opposition groups in Idlib would remain in areas where they were already present, while Russian Federation and Turkey would carry out joint patrols in the area to prevent a resumption of fighting. The Anadolu Agency reported no damage or injury in the incident, which involved a different Turkish post than that in Morek.
Kalin said there was "no question" of moving one of its 12 observation posts in Idlib, despite it being cut off from the rest of the province by the advance of Syrian forces this week.
Syrian Foreign Minister Walid al-Moallem vowed that Damascus will not stop combatting insurgents until all of Syria comes under government control.
On Thursday, Syrian warplanes carried out air strikes on towns and villages north of Khan Sheikhoun, including the town of Maaret al-Numan, according to opposition activists.
It added that the militants have withdrawn from regions in Southern Khan Sheikhoun and the towns in Northern Hama, including Kafar Zita, al-Latamineh and Murak, noting that the fate of a Turkish watchtower in Murak is unknown.
Souran, located in Hama's northern countryside, is considered the first line of defence for government forces stationed on the doorstep of the city of Hama.
Local sources in Khan Sheikhoun in Southern Idlib reported that the terrorists have fully withdrawn from the town for the fear of being surrounded by the Syrian army.
Syrian troops have been on the offensive in Idlib and nearby areas since April 30, forcing more than half a million people to flee their homes and leaving more than 2,000 people dead, including hundreds of civilians.