Syrian rebels stormed an air defence base in the north of the country on Tuesday, opposition sources said.
The fighters had captured more than half the base at Sheikh Suleiman, 18 km (11 miles) from the Turkish border and 30 km (20 miles) northwest of the contested city of Aleppo, and fighting was still taking, rebel and opposition sources in the area said.
"The fighters have taken three artillery pieces and have entered most of the base. Fighter jets are flying over the area to try and force them out," said Abu Mujahed al-Halabi, an activist with the opposition Sham News Network.
With severe restrictions by Syrian authorities on non-state media, independent verification of the report was not possible.
A rebel source said the fighters took large stocks of explosives from the site and will withdraw quickly to avoid the retaliatory air strikes that have blunted their advance across the country.
"Assad's forces use the base to shell many villages and towns in the countryside. It is now neutralised," the source said.