Members of the Syrian Free Army gained control over a military base in the northern town of Daret Ezzah after heavy fighting with government troops.
The rebels said they co-ordinated the attack with a group of defectors inside the base 30 miles northwest of Aleppo province.
"The Free Army battalions in western rural Aleppo liberated the battalion 1041 in the area of Jabal al Sheikh Barakat in the town of Daret Ezzah," army defector Abu Jehad said.
"Thank God, we have full control over the location with the help of defecting soldiers from inside the battalion. We seized all artillery including anti-aircraft systems and light personal weapons,"
Gunmen stormed a pro-government Syrian TV channel headquarters on Wednesday, bombing buildings and shooting dead three employees, state media said, in one of the boldest attacks yet on a symbol of the authoritarian state.
President Bashar al-Assad declared late on Tuesday that his country was "at war". U.S. intelligence officials said the Syrian regime was "holding fairly firm" and digging in for a long struggle against rebel forces who are getting stronger.
The dawn attack on Ikhbariya television's offices, located 20 km (15 miles) south of the capital, as well as overnight fighting on the outskirts of Damascus showed 16 months of violence now rapidly encroaching on the capital.
"We live in a real state of war from all angles," Assad told a cabinet he appointed on Tuesday, in a speech broadcast on state television. "When we are in a war, all policies and all sides and all sectors need to be directed at winning this war."
The declaration marks a change of rhetoric from Assad, who had long dismissed the uprising against him as the work of scattered militants in "terrorist gangs" funded from abroad.
The rambling speech - Assad also commented on subjects as far afield as the benefits of renewable energy - left little room for compromise. He denounced the West, which "takes and never gives, and this has been proven at every stage".