Syrian rebels battled regime troops inside the Minnigh military airport in the north of the country for the first time on Wednesday, the Syrian Observatory for Human Rights said.
"The rebels, who have laid siege to the airport for months now, entered it for the first time around dawn," Observatory director Rami Abdel Rahman told AFP.
"Heavy fighting is still taking place this morning inside the grounds of the airport," he said.
On Tuesday, the rebels took a key military position outside the airport, in Aleppo province, which allowed them to launch a raid on it.
A group of regime-allied fighters who attempted to reach the airport to boost government troops there were intercepted by Kurdish fighters who killed nine of them, the Observatory said.
A military source said the rebels broke into the airport on Tuesday but added that they were then pushed back out.
Rebel fighters have tried repeatedly to take the key airfield.
Since the beginning of the year, rebel forces have been fighting what they call the "battle of the airports in Aleppo" in a bid to deprive the regime of a key supply route.
Rebels have set their sights on the Aleppo international airport, along with the Jarrah, Kwiyres, Minnigh and Nayrab military fields. They took the Jarrah military airport on February 12.
Meanwhile, in Jaramana, a mainly Christian and Druze suburb of Damascus squarely under regime control, at least seven civilians were killed by two mortar rounds that struck near the municipality building and two schools, said the Observatory.
Another 30 people were wounded, six of them critically, it added.
State news agency SANA published the same toll.
Wednesday's violence comes a day after at least 123 people were killed in violence across Syria, said the Observatory. Among them were 61 civilians, 47 rebels and 15 soldiers.