Syria's opposition has begun to take aim at government airbases, making less effective government airstrikes that had been the biggest threat to rebels.
The opposition, which has long been outgunned by the government, boasted that they have until Friday surrounded four airports in Syria's northern commercial hub of Aleppo province, managing to reduce air traffic by firing heavy machine guns.
The opposition hoped their campaign would to some extent chip away at government superiority in the air, said opposition sources.
The government, which has lost control of several parts of the country, was becoming increasingly dependent on airstrikes. Losing control of airports would have serious consequences for the government.
Despite the advances in the north of the country, the rebels, however, are not able to stop government airstrikes, most of which are carried out by jets from elsewhere in the country.
The Britain-based Syrian Observatory for Human Rights said more than a dozen people were killed on Friday in a government airstrike in al-Safira, a town south of Aleppo.
The airstrike was reportedly in retaliation for weeks of rebel assault on a government military complex located next to the town.
Meanwhile, with the rebels advancing steadily in the second half of 2012 and claiming to have moved into the second phase in their battle to "liberate Damascus," chances of a political solution to the 21-month-old crisis have become smaller.
Mouaz al-Khatib, head of the six-week-old Syrian National Coalition for Opposition and Revolutionary Forces, which has been recognized by most Western and Arab states as the legitimate representative of the Syrian people, has turned down an invitation for talks by Moscow, which has been intensifying its mediation moves.
The opposition leader insisted on the ouster of Syrian President Bashar al-Assad as the precondition to any negotiations, while Russia proposed inclusive inter-Syria dialogue and political process to end the crisis.
"We have clearly said we will not go to Moscow. We could meet in an Arab country if there was a clear agenda," said al-Khatib.
He indicated that the invitation meant Moscow has somewhat accepted the fact that his organization is the legitimate representative of the Syrian people.
"If we don't represent the Syrian people, why is he (Moscow) inviting us?" al-Khatib asked at the Qatar-based Al-Jazeera TV.
At the same time, UN-Arab League joint envoy Lakhdar Brahimi has been conducting shuttle diplomacy, bringing with him a plan to form a transitional government with "full executive powers."
However, as the plan did not say whether the transitional government would include Assad or his allies, it is unlikely to be accepted by the opposition, whose leverage has been largely boosted by victories on the battlefields.
Brahimi, who had met Assad and representatives of the opposition groups during his stay in Syria, is expected to travel to Moscow to meet Russian Foreign Minister Sergei Lavrov on Saturday.