Syrian rebels have killed at least 18 soldiers in the northwestern town of Saraqeb, in Idlib province, by setting off a car bomb outside a military position and then attacked it, according to a watchdog group.
Rami Abdul Rahman, head of the UK-based rights group Syrian Observatory for Human Rights (SOHR), said on Wednesday the details of the incident were still sketchy, and that he could not say whether the car bombing was a suicide attack.
"There were 70 to 100 soldiers there when the attack occurred" in Saraqeb, he said.
"Twenty soldiers escaped, and clashes are still going on."
In-depth coverage of escalating violence across Syria
Outside Aleppo, Syria's second city, fighting erupted at dawn in the Nayrab area, around 5km from the airport,which remained fully operational.
Over the past several weeks, rebels have taken to attacking military airfields in an attempt to prevent them from being used for launching air raids while commercial facilities have been left alone.
However, this is not the first time there has been fighting around Aleppo airport, which serves the country's commercial capital, where the army shelled a string of neighbourhoods.
Elsewhere, a boy and a girl were killed and dozens of civilians wounded when the army shelled the rebel village of Latamneh in Hama province, according to the SOHR, which gathers its information from a wide network of activists.
Also in Hama, the SOHR reported that eight bodies had been found in farmlands in Halfaya village, following an assault by government forces. It said the number of dead was expected to rise as many people were reported missing.
Against this backdrop of continued violence in Syria, Philip Hammond, UK defence secretary, said in the Qatari capital Doha on Wednesday that Western countries are not considering military intervention in Syria while Russia and China oppose such action.
"So long as two major powers are actively opposed to any intervention in Syria, that is a major impediment to Western nations contemplating such action," he said in a clear reference to Russia and China.
Both powers have repeatedly opposed UN action against Damascus.
Meanwhile, Lakhdar Brahimi, international peace envoy, was in Cairo on Wednesday to meet exiled opposition leaders in advance of a planned visit to Damascus.
Ban Ki-moon, the UN chief, said Brahimi would meet Syrian President Bashar al-Assad in the Syrian capital on Thursday and insisted that "the violence must stop by both sides".
He said in Bern that he understood the frustration felt by many in the face of the UN Security Council's apparent paralysis in dealing with the spiralling crisis.
But "while we may be frustrated and troubled by not being able to address the situation in Syria, which has reached intolerable circumstances", he said, "we should not be overly pessimistic about the strength and the commitment of the international community, especially the international organisations".
Coupled with the violence is the humanitarian crisis caused by the large number of people fleeing the country or displaced within its borders.
The UN refugee agency says the number of civilians who have fled nearly 18 months of violence has reached more than 250,000. And it says more than 1.2 million civilians, more than half of them children, have been displaced inside Syria.
Angelina Jolie, Hollywood film star and UN special envoy, will travel to Turkey on Thursday to visit Syrian refugee camps near the border.
Jolie visited Syrian refugees in Lebanon on Wednesday as well as a refugee camp in Jordan on Tuesday, where she appealed to the world to "do everything they can to support these refugees" fleeing the escalating unrest.