Rebels on Tuesday overran a military air base and captured warplanes, gaining ground in northern Syria for a second straight day as the UN said the death toll from the 23-month conflict was nearly 70,000.
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 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 ever more clear that the regime's insistence on an imminent victory is false," he told AFP.
Assad meanwhile called for "collective action" by the state and Syrian people to limit the effects of the crisis, state news agency SANA reported.
The Syrian president also accused "groups that target Syria" of trying to destroy the country's infrastructure.
The conflict has killed nearly 70,000 people since it erupted in March 2011, UN rights chief Navi Pillay said, only a month after putting the toll at 60,000.
Pillay also condemned the inaction of the UN Security Council, where China and Russia have used veto powers to block three resolutions that would have threatened sanctions against Assad's regime.
"We will be judged against the tragedy that has unfolded before our eyes. This council, as well of those of us in key positions within the UN, will be rightly asked what we did," she said.
Her comments after the UN's Ban urged Damascus to view an offer for talks with National Coalition chief Ahmed Moaz al-Khatib as "an opportunity we should not miss -- a chance to switch from a devastating military logic to a promising political approach".
Ban also said the Security Council "must no longer stand on the sidelines, deadlocked, silently witnessing the slaughter".