Syrian rebels launched deadly attacks on the military on Saturday in a campaign increasingly targeting its air power, as President Bashar al-Assad's traditional ally Russia said it was "naive" to expect him not to fight back.
Rebel fighters captured the main air defence building in Albu Kamal on the Iraqi border, the Syrian Observatory for Human Right said, adding that "preliminary reports" suggested they had seized ground-to-air missiles that could boost their ability to down government aircraft.
The assault late Friday came hot on the heels of a rebel attack on the Abu Zohur air base in Idlib province in the northwest, where the Free Syrian Army said it downed a MiG warplane shortly after takeoff earlier this week.
With the insurgency intensifying, Russian Foreign Minister Sergei Lavrov said calls by Western and Arab governments for Assad to unilaterally pull back his troops amounted to a demand for "capitulation" that they had no right to make.
In their assault in Albu Kamal, rebel fighters also captured 16 air defence personnel and attacked the nearby Hamdan air base, the Syrian Observatory said.
The seizure of the air defence headquarters was a "major coup" for the rebels, the Britain-based watchdog's director Rami Abdel Rahman told AFP, adding that it sparked retaliatory shelling in the town of some 60,000 people that killed at least five civilians.
They were among a total of 125 people killed in violence nationwide on Friday -- 74 civilians, 29 soldiers and 22 rebels, according to the Observatory's figures.
The rebels claim to have destroyed a dozen aircraft on the ground in their attacks on air bases in recent days as they seek to counter the government's use of MiG warplanes and helicopter gunships against them.
In Idlib province, a major battleground on the Turkish border, rebels attacked an army roadblock in the Harem district early Saturday, killing or wounding nine soldiers, the Observatory said.
In the central province of Hama, rebels killed at least four soldiers in a similar attack, it added.
In talks with Syrian Prime Minister Wael al-Halaqi in Tehran on Friday, UN chief Ban Ki-moon said that Assad's regime must stop using its heavy weapons.
But the Russia's top diplomat said on Saturday that such calls were "completely unrealistic".
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"Either people are naive or it is some sort of provocation," he added.
Lavrov stressed that Moscow, a Cold War era ally of Damascus, was not trying to support Assad or his government but basing its policies on the daily situation on the ground.
"No matter your view of the Syrian regime, it is completely unrealistic in the current situation -- when there is fighting in the cities -- to say that the only way out is the unilateral capitulation of one of the opposing sides," he said.
"We are not holding on to any regime or any individuals in the Syrian situation. We are simply basing our position on what is realistic."
Both Damascus and Aleppo -- Syria's two largest cities -- have seen persistent fighting between troops and rebels in a conflict that has now claimed more than 26,000 lives since March last year, according to the Observatory's figures.
The International Committee of the Red Cross has warned that the situation across large swathes of Syria is "edging towards irreversible deterioration".
Turkey has been pressing for the establishment of safe havens inside Syria to stem the mounting exodus of refugees, and reacted with frustration when its calls fell on deaf ears at the UN Security Council on Thursday.
But on Friday Turkish Prime Minister Recep Tayyip Erdogan acknowledged that any such move would require UN backing and would be far too risky without the prior establishment of a no-fly zone.
"We cannot take such a step without any resolution at the UN Security Council," Erdogan said.
"You cannot create a buffer zone without a no-fly zone in place," he added.
Turkey is home to more than 80,000 refugees and thousands more have been stranded on other side of the border waiting to be accommodated in camps yet to be built by the Turks.
To the anger of Damascus, Turkey also plays host to large numbers of defecting Syrian soldiers who formed the kernel of the Free Syrian Army, although it has repeatedly denied providing the rebels with weapons.
"Most of the terrorists in Syria come from Turkey," Syrian Deputy Foreign Minister Faisal Muqdad charged on Friday.