Rebels on Tuesday overran a military air base and captured warplanes, 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 at Al-Jarrah 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 dozens of troops, the Britain-based watchdog said, adding that as the rest of the troops pulled out, they left behind ammunition and warplanes.
Soon afterwards, the air force used fighter jets to bombard the airport to try to dislodge rebels there, the Observatory said, adding warplanes also carried out raids near the international airport which has come under a rebel assault.
Speaking to AFP on condition of anonymity, a military source in Aleppo confirmed the rebel capture "after 48 hours of fierce combat", but downplayed the importance of Al-Jarrah.
"It is a very small airport, used for training purposes," he said. "There are only small amounts of unusable ammunition left there, and several planes that have long been out of action."
Activists meanwhile reported the launch of rebel offensives on the Aleppo international airport and Nayrab military airport nearby, although the military source denied any such assaults.
Closed since January 1, "Aleppo's international airport has in the past suffered attacks, but tightened security measures and the Syrian army's bravery has stopped armed men from getting anywhere near there," said the army source.
The Observatory also reported a rebel capture of the main road linking Aleppo province to neighbouring Raqa and parts of a military base tasked with securing the area's airports.
Activists in Aleppo have told AFP that fighters in the north have shifted their focus from city battles 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.
Though the rebels have yet to take a major city in the war-ravaged country almost two years into the revolution, advances in northern Syria were remarkably speedy on Tuesday, the Observatory's Rami Abdel Rahman said.
"After events in Aleppo on Tuesday, it became clear ever more clear that the regime's insistence on an imminent victory is false," he told AFP.
Assad meanwhile on Tuesday called for "collective action" by the state and Syrian citizens to limit the effects of the country's crisis, state news agency SANA reported.
Assad also accused "groups that target Syria" of trying to destroy the country's infrastructure.
His comments came as the UN's Ban urged Damascus 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.