Russia warns the US and its allies that it will shoot down any aircraft flying west of the Euphrates river.
Fighting between government forces and opposition fighters has intensified in the Quneitra province in Syria’s south, situated in the 30 percent part of the Golan Heights under Syrian control.
More than a dozen people were killed, including both pro-government forces and opposition fighters, in the latest increase in fighting in the countryside of al-Baath city and near the town of Khan Arnab, the Syrian Observatory for Human Rights (SOHR) said on Sunday.
The deaths came as the al-Qaeda-linked Levant Liberation Committee [Hayat Tahrir al-Sham] and allied anti-government groups launched an offensive to take control of al-Baath city, one of the few towns in the province that has remained under control of Syrian government forces in recent years.
Abu Omar al-Jolani, a Quneitra-based media activist, told Al Jazeera that “the battle is ongoing” and that armed groups “managed to break the regime’s first line of defence”.
Also on Sunday, Israeli fighter jets targeted Syrian government positions in the region for a second day in a row, reportedly destroying a handful of tanks.
The UK-based SOHR reported that the strikes killed two Syrian army soldiers and injured several others.
Israel has been occupying roughly 70 percent of the Golan Heights since the 1967 Middle East war.
Since the outbreak of fighting in the Golan region in 2012, it has carried out sporadic air strikes, mostly targeting government forces and their allies.
In recent months, President Bashar al-Assad’s forces, backed by Russian air power, have gained ground in Syria from opposition fighters and armed groups.
Since the war began in 2011, it has killed hundreds of thousands, driven millions more from their homes, caused a global refugee crisis and drawn in regional and world powers.
The conflict is far from over. Opposition fighters hold large expanses of the country, including around Idlib province near Hama, and launched a new attack in Quneitra in the southwest on Saturday.
Anti-government fighters also hold the Eastern Ghouta area near Damascus, parts of the desert in the southeast and a large pocket south of Hama around the city of Rastan.
As recently as March, opposition fighters advanced from Idlib province to within a few miles of Hama, before the army and its allies pushed them back in weeks of fierce fighting.
However, the army drove the fighters from their biggest urban stronghold in Aleppo in December and have also forced several important opposition enclaves to surrender over the past year.
US-led coalition air raids have also caused large numbers of civilian casualties, according to the SOHR.
It said on Saturday that coalition air strikes in and around Raqqa, the besieged stronghold of the Islamic State of Iraq and the Levant (ISIL) group, have killed nearly 700 civilians so far this year.