Wearing a white headscarf and a traditional black cloak, the Iraqi tribal sheikh addressed his peers: "We're all in the same boat, the (Islamic) State is our state."

"We say to our families that our swords and those of our brothers, the soldiers of the (Islamic) State are directed against the same enemy," he said in a video released by IS, addressing some 30 tribal figures, some clutching Kalashnikovs.

The Turkish army has called a meeting of troop commanders stationed along its fortified border with Syria to discuss a possible intervention in Syria, the Hurriyet newspaper reported on Sunday. 

Turkey has boosted its military defenses on the volatile border over the past week, stationing tanks and anti-aircraft missiles there as well as bolstering troop numbers, as fighting between Islamist-led groups and Syrian regime forces in the northern city of Aleppo has intensified. 

Syrian government forces backed by fighters from Hizbullah entered the town of Zabadani on Sunday in a bid to take the last rebel-held bastion along the Lebanese border.

Syrian state television and Hizbullah's al-Manar station announced the advance into Zabadani on Sunday, a day after a major operation against it began.

A U.S.-led coalition has carried out some of its heaviest air strikes yet on the Islamic State group's de facto Syrian capital, killing more than 30 people, including six civilians.

The U.S.-led coalition said it carried out 18 air strikes against IS' de facto Syrian capital of Raqa, destroying vehicles and bridges.

The army has the situation along the Lebanese-Syrian border under control, reassured a military source to the daily al-Mustaqbal on Sunday.

It told the daily: “The border is under control and the military is performing its duties to the fullest, leaving no room for the gunmen.”

The Islamic State group on Saturday released a video showing 25 Syrian government soldiers being executed by teenagers in the ancient amphitheater in the city of Palmyra.

The video documented an execution that reportedly happened shortly after the jihadist group captured the city on May 21.

Syrian troops backed by members of Hizbullah began a major offensive Saturday under the cover of intense airstrikes to retake a rebel-held mountain resort while opposition fighters retaliated by shelling the capital Damascus.

Taking the rebel-held town of Zabadani would tighten Hizbullah's grip on Syrian territories bordering Lebanon and would strengthen the Syrian government's control over of the Beirut-Damascus highway.

Two coalitions of Syrian rebels battled to advance in government-held western Aleppo Saturday, seizing an army barracks in one district, but being pushed back elsewhere.

The fighting in the country's former economic powerhouse is some of the fiercest since the Syrian conflict arrived in the northern city in mid-2012.

A new Islamist rebel alliance, including al-Qaida's Syrian affiliate, was locked in a fierce battle Friday to seize government-held areas of Aleppo, the divided former economic capital.

Once a powerhouse of industry, Aleppo has been devastated by years of fighting between regime forces and a succession of rebel groups.

Turkey has no plans to intervene militarily in Syria anytime soon, Prime Minister Ahmet Davutoglu said, refuting media speculation about an imminent operation to create a buffer zone along the Turkish-Syrian border.

"No one should expect that Turkey will go into Syria tomorrow or in the near future. It's speculation," Davutoglu told the private Kanal 7 broadcaster in an interview late Thursday.