At least six air strikes carried out by Russian warplanes on Sunday hit rebel-held northwestern Syrian city of Idlib killing more than 43 people and wounding 151, pro-opposition media said.
Local residents said that the air strikes have targeted a busy market in the city center and other residential areas destroying buildings.
Rescue workers reported that there are at least 30 more bodies under the ruins as the process to retrieve them was still ongoing.
"There are a lot of corpses under the rubble," Yasser Hammo, a civil defence worker, said by an Internet messaging system.
Since September 30, Russia has been launching air strikes in support of Syrian regime leader Bashar al Assad. The Russian air strikes have targeted assemblies of Assad opponents, including the western trained moderate opposition, killing hundreds of civilians and destroying facilities in the western rebel-held areas despite announcing that the target of their campaign is DAESH.
The Syrian Observatory for Human Rights (SOHR) confirmed that the attacks were conducted by Russian warplanes. SOHR says it distinguishes between Syrian, Russian and US-led coalition aircraft depending on the type of planes and ordinance used and whether the planes took off from inside the country.
However, residents also say they are able to differentiate the Russian fighters from the regime aircraft, which usually fly low altitudes dropping barrel bombs.
The city of Idlib, which was once the main regime stronghold in northwestern Syria was taken by alliance of rebel groups dubbed Fateh Army earlier this year, after fierce battles with regime forces.
Russia has two military bases in Syria located in two coastal provinces of Latakia and Tartus, where Russia is expanding its only naval repair base in the Mediterranean, which is key to Russia maintaining any kind of substantial naval presence in region.
In September, a ceasefire brokered by the UN was announced in two villages - Kafraya and Fouaa- in Idlib and Kasab a border town near Lebanon. According to the truce, rebel fighters were allowed to withdraw from Kasab in return for the evacuation of Shiite civilians in the two towns in Idlib province.
The war in Syria started in 2011, after peaceful demonstrations demanding freedom and better living conditions were suppressed by the Syrian regime. Since the early beginning of the crisis in Syria, Russia and Iran have been supporting Assad and forces loyal to him.
The Syrian conflict paved the way for the emergence of the terrorist group DAESH which declared the formation of a self-proclaimed caliphate in Syria and Iraq in 2014 with the Syrian city of Raqqa as its capital. A US-led coalition launched an aerial campaign to fight the group in September 2014.
Earlier this week, a peace process in Syria was outlined by a resolution adopted unanimously by the UN Security Council.
Since the beginning of the conflict, more than 250,000 people have been killed according to UN estimates, while the SOHR says that the true death toll exceeds 350,000.