Syrian troops bombarded the outskirts of Damascus, where monitors said almost 50 people died in a battle for a military airport on Sunday, AFP reported.
Russia and France, meanwhile, prepared for talks on Tuesday in Paris at which Russian Prime Minister Dmitry Medvedev and France's President Francois Hollande are expected to address differences over the Syria conflict.
"There is a major disagreement," Russia's envoy to Paris, Alexander Orlov said. "The West says (a solution) must start with the departure of (President) Bashar al-Assad, and we say this is where it must end."
Turkey and close Syria ally Iran, whose positions on the crisis are also diametrically opposed, held closed-door talks on Saturday.
No details were published after a two-hour meeting in Istanbul between Iran's parliament speaker Ali Larijani and Turkish Prime Minister Recep Tayyip Erdogan, whose country Tehran accuses of arming the rebels.
World powers have made no progress on finding a political solution to the conflict, with Russia and China blocking UN Security Council efforts to ratchet up the pressure on Damascus.
On the ground Sunday, rebels captured a "large part" of the military airport of Marj al-Sultan, nine miles east of Damascus, and destroyed two helicopters overnight, the Syrian Observatory for Human Rights said.
The Britain-based monitoring group told AFP that 31 rebels and 16 soldiers were killed in the battle.
Meanwhile, regime helicopter gunships pounded the northeast and southwest outskirts of Damascus as clashes also spilled over into southern districts of the capital, the Observatory said, giving a preliminary toll of 28 people killed in Damascus province on Sunday.
In northern Syria, rebels pressed on with an offensive against troops stationed at the strategic Tishrin dam, which straddles the Euphrates River and connects the provinces of Aleppo and Raqa.
Rebels already control one of the main routes to Raqa, and the dam would give them a second passage, connecting a wide expanse of territory between the two provinces, both of which border Turkey.
Insurgents also surrounded the military airport of Deir Ezzor city in the east, where four rebels and a civilian were killed in clashes, sniper fire and shelling.
The army has already lost much of the eastern part of Deir Ezzor province, which borders Iraq. Just over a week ago, the rebels seized control of a military airbase in the border town of Albu Kamal.
In the southern province of Daraa, insurgents took control of a military outpost on the border with Jordan overnight, but later vacated the area for fear of air strikes that regularly follow rebel gains, the Observatory said.
Meanwhile, it said, five people died in a bus explosion in the province.
Nearly a week ago, the fragmented opposition forces who had managed to unite into a council to form a government-in-exile instead split in half, with 13 Muslim extremist groups forming their own secessionist movement.
The Muslim group stated its distaste for the internationally-supported, “secular, foreign-controlled” Syrian National Council and instead declared an independent Islamic state in the northern commercial city of Aleppo.
The Syrian National Council has been recognized by the United States as the “legitimate representative” of the Syrian people. France went even further, saying the coalition would be considered by Paris as the sole legitimate representative of the Syrian people.