Syrian regime forces edged forward in the northern province of Aleppo on Saturday with air cover from Russian warplanes, but faced fierce resistance from rebel forces in the country's center.
Since Moscow began its air campaign in support of its Damascus ally on September 30, the army and its allies have launched four ground offensives against rebel forces in northern and central Syria.
Syrian troops have gone on the attack in Aleppo, Hama, Homs and Latakia provinces taking advantage of Russian air strikes against Al Qaeda affiliate Al-Nusra Front and other rebel groups.
Three senior Nusra members, one of them a US-designated "global terrorist", were killed in an air strike in Aleppo province on Thursday, a monitoring group said.
Regime forces control the western part of Aleppo city – Syria's pre-war economic hub – but much of the surrounding province is held by rebel groups – Al-Qaeda and others in the west and ISIS in the east.
Troops seized at least five villages and several strategic hilltops on Saturday, bringing them to the edges of Al-Hader, 25 kilometers (15 miles) south of Aleppo city, the Syrian Observatory for Human Rights said.
"Taking this village would allow the regime to secure a supply line for the army between Aleppo and the central province of Hama, and would put the rebel's own supply route in their line of fire," Observatory director Rami Abdel Rahman said
He said that over the previous 24 hours, 17 rebels and eight pro-regime fighters had been killed, while around 2,000 families had fled the fighting.
Russia 'defending interests'
And according to Maamun al-Khatieb, an activist in Aleppo, Russian warplanes had carried out at least 80 air raids on the area since Friday morning.
A US official said as many as 2,000 fighters from Iran and its regional allies were supporting the army's offensive in coordination with Russia.
A Syrian military source said troops had also advanced to within six kilometres (less than four miles) of Kweyris military airport, east of Aleppo city, which has been under siege by fighters of the Islamic State group (ISIS).
If the army secures the airbase, it could be used by Russia planes – currently flying out of the Hmeimim base in Latakia province on the Mediterranean coast – to launch strikes, the Observatory said.
Russian Prime Minister Dmitry Medvedev said Moscow's air war was an attempt to protect its own national interests and security, amid reports that thousands of fighters from the former Soviet Union are fighting with ISIS in Syria.
"Of course we are not fighting for specific leaders, we are defending our national interests, on the one hand," Medvedev said.
"And secondly, we have a request from the lawful authorities (of Syria). That is the basis we are working on," he said.
"The president (Vladimir Putin) said this: it's obvious that if we don't destroy these terrorists there, they will come to Russia."
Fresh Russia strikes
Around 200 people demonstrated in Moscow on Saturday against Russia's air campaign, with police arresting one woman with a banner reading, "Putin assassin, don't bring shame on Russia."
Syria's opposition coalition on Saturday called for "urgent action to put an end to the Russian aggression."
Meanwhile, Russian Deputy Foreign Minister Mikhail Bogdanov met with Egyptian Foreign Minister Sameh Shoukri in Cairo, agreeing "to intensify efforts to effectively counter the menace posed by IS", a Russian ministry statement said, using an alternative acronym for ISIS.
Russia's military said it is continuing to use its drones over Syrian territory, despite suspicions that one of its drones was downed by Turkey the previous day.
"I would … like to emphasize that Russian drones are continuing to monitor the situation in Syria's skies," spokesman Igor Konashenkov said, quoted by RIA Novosti news agency.
The defense ministry said its latest strikes in Syria hit 49 targets in Hama, Idlib, Latakia, Damascus and Aleppo provinces.
But as regime forces pushed ahead in Aleppo, they faced resistance in the central province of Homs.
Troops have been trying to seize the village of Talbisseh, controlled by non-jihadist rebels in an enclave north of government-held Homs city.
The Observatory said Saturday nine Russian air strikes had struck Talbisseh and its surroundings, where regime forces were locked in heavy fighting despite the air support.
Since the offensive began on Thursday, at least 72 people have been killed in Homs province, nearly half of them civilians, the Observatory said.
In total, more than 250,000 people have been killed in the Syrian conflict since it began in March 2011.