Rebels on Tuesday overran a military air base, a watchdog said, a day after seizing control of Syria's largest dam as they pushed an assault on strategic targets in the north of the country.
The military advance came as prospects for a political solution to Syria's civil war faded and as UN Secretary General Ban Ki-moon urged President Bashar al-Assad's regime to accept an offer of dialogue by an opposition leader.
The Syrian Observatory for Human Rights said the rebels captured a military airport in Al-Hajjar in Aleppo province, and in the process seized for the first time a fleet of deployable warplanes including MiG fighter jets.
During their assault on the airport, the rebels killed, injured or imprisoned some 40 troops, the Britain-based watchdog said.
"The remainder of the troops pulled out from the airport, leaving behind several warplanes and large amounts of ammunition," Observatory director Rami Abdel Rahman told AFP.
Rebels also launched offensives on other airports in the region, activists said.
"At dawn Tuesday, several rebel battalions launched simultaneous assaults on Aleppo international airport and Nayrab military airport," the grassroots anti-regime Aleppo Media Centre said via Facebook.
The international airport at Syria's second city has been closed since January 1.
Activists in Aleppo have told AFP that fighters in the north have shifted their focus to the capture of military airports and bases.
"They are important because they are an instant source of ammunition and supplies, and because their capture means putting out of action the warplanes used to bombard us," Aleppo-based activist Abu Hisham said via the Internet.
But while the rebels have notched up victories in northern and eastern Syria they have yet to take a major city in the war-ravaged country, which is largely art a military stalemate almost two years into the revolution.
The capture of Al-Jarrah airport came just over a month after rebels overran Taftanaz airbase, the largest in northern Syria.
Amateur video shot by rebels overrunning Al-Jarrah and distributed via the Internet showed a fleet of warplanes lining the airport's runways.
"Thank God, Ahrar al-Sham (Islamist rebels) have overrun the military airport" at Al-Jarrah, said an unidentified cameraman who shot a video at the site.
"MiG warplanes are now in the hands of Ahrar al-Sham. And here is the ammunition," the cameraman added, filming two Russian-made fighter jets similar to those used by the army since last summer to bombard rebel targets.
The authenticity of the video was impossible to verify.
The battlefield assaults came just hours after the UN's Ban urged Assad's regime to view an offer for talks with Syrian National Coalition chief Moaz al-Khatib as "an opportunity we should not miss -- a chance to switch from a devastating military logic to a promising political approach".
Speaking at the Council on Foreign Relations in New York, Ban described as "courageous" Khatib's offer for talks.
Khatib said in late January he was prepared to hold direct talks with regime representatives without "blood on their hands," on condition the talks focus on replacing Assad.
The Assad regime has said it was open to talks but without conditions attached.
The UN Security Council, currently divided over Syria, "must no longer stand on the sidelines, deadlocked, silently witnessing the slaughter," said Ban.
According to UN figures, more than 60,000 people have been killed in violence across Syria since the eruption of an anti-Assad revolt in March 2011.
As well as lives lost, the raging conflict has caused massive infrastructural and economic damage.
On Tuesday, Syria's state news agency SANA cited electricity minister Imad Khamis as saying widespread blackouts have caused economic losses of around $22 billion since March 2011.
Supporters of Assad's regime meanwhile planned a demonstration for next Tuesday in Damascus, under the slogan "resistance against terrorism", using the authorities' term for rebels.
The Observatory said at least 137 people were killed in violence across the country on Monday. Among them were 49 civilians.