Rebels launched a counter-attack against Syrian government forces and their allies in Idlib province on Thursday, trying to roll back an advance that is fuelling tension with neighbouring Turkey. The operations also aim to secure the road linking the capital, Damascus, with Aleppo, Syria's largest city.
The government-controlled Syrian Central Military Media said troops were engaged in fierce fighting with al-Qaida-linked militants and other insurgents just outside Abu Zuhour.
The government offensive has displaced tens of thousands of people who fled toward areas close to the Turkish border.
The push into Idlib province, the largest remaining territory held by rebels in Syria, is the deepest by the government since it lost much of the area three years ago.
The Russian Defense Ministry did not confirm claims posted on some websites about destroyed airplanes in the Russia-operated Hmeimim air base in Syria on New Year's Eve but on January 5, Russian officials did say two soldiers had been killed in a rocket attack.
Russia's Defense Ministry meanwhile said its air base and naval station in western Syria came under at least 13 attempted attacks by drones since Saturday.
One, a mother of twins, said she had initially left one of her children behind in the panic to escape the air strikes. Assad has defeated rebels in many parts of western Syria with critical help from Russian Federation and Iran.
Turkish presidential sources said that President Recep Tayyip Erdogan spoke to his Russian counterpart Vladimir Putin on the phone Thursday and told him that Moscow should stop Syrian attacks on its opposition in Idlib and eastern Ghouta near Damascus, if he wants peace negotiations to succeed. The woman was so frightened, she initially left one of her children behind. "The fear affected our brains", the IRC quoted her as saying.
The IRC said almost two thirds of the displaced in Idlib are living in makeshift tents that are unable to withstand winter conditions while others live in abandoned or partially-build homes that have well water but no toilets.
State media did not report any blasts in the area. The Observatory says 159 rebels and government soldiers have been killed in fighting over the base since December 29.
At least 400,000 people have been killed and half of Syria's population displaced since a violent crackdown on anti-government demonstrations in 2011 plunged the country into civil war. The U.S. Treasury Department says its sanctions against the Syrian government are in response to human rights abuses and state-sponsored terrorism.