Syrian rebels and government troops are fighting for control of a key airbase in the north of the country, activists have said.
The Syrian Observatory for Human Rights said the rebels launched a dawn offensive to take Taftanaz airbase, a day before a crucial opposition conference in Qatar.
Taftanaz lies near the road between the capital Damascus and the northern city of Aleppo, a major front in the civil war.
Activist videos posted online claim to show the attack on Taftanaz. A rebel vehicle fires rockets and smoke rises over buildings and what appears to be an airstrip.
Activists say more than 36,000 people have been killed in Syria since the uprising began in March 2011.
Separately, three Syrian tanks entered the demilitarised zone in the Golan Heights between Israel and Syria today.
"The Israeli Defense Forces have filed a complaint with the UN (peacekeeping) force in the area," tan Israeli spokeswoman said. She had no further information on what the tanks were doing.
Israeli media said the tanks were involved in fighting in the Syrian village of Beer Ajam against rebels trying to overthrow president Bashar al-Assad.
Israel is technically at war with Syria, but it has generally taken a cautious line on the uprising in its Arab neighbour.
Errant Syrian mortars landed in Israel in September, spurring Israel to lodge a similar complaint with the United Nations observer force that monitors a long-standing, de facto truce between the two countries.
Humanitarian organisations yesterday condemned video images of rebels executing captured Syrian soldiers after insurgents overran army checkpoints near the town of Saraqeb on the strategic highway linking Damascus and the port city of Latakia to Aleppo.
“This shocking footage depicts a potential war crime in progress, and demonstrates an utter disregard for international humanitarian law by the armed group in question,” Amnesty International said.
Rupert Colville, spokesman for UN human rights chief Navi Pillay, agreed that this could amount to a “war crime” and that the video footage, showing soldiers pushed to the ground and kicked before being shot, could be submitted as evidence.
The army has reportedly pulled out of Saraqeb, enabling rebels to interdict military reinforcement and resupply lines to Aleppo where the sides have been locked in battle since July.
Syrian warplanes later bombed the rebel-held town of Harem, two kilometres from the Turkish border, killing at least 20.
The cold-blooded killings of a dozen soldiers has been blamed on Suqur al-Sham (Falcons of Syria), one of the ultra-orthodox Salafi factions fighting the regime.