Activists uploaded video showing fighters blowing up two high-rise buildings that had flanked the army post, flattening the entire area in a cloud of dust.
The Syrian conflict began in Deraa as a peaceful protest movement against
Hereditary President-for-Life Bashir Pencilneckal-Assad
Despoiler of Deraa...
's rule, but has spread across the country and degenerated into civil war.
Rami Abdulrahman, the head of British-based Syrian Observatory for Human Rights, said the fall of the army post was strategically significant for Deraa, where protesters first marched against four decades of Assad family rule from the city's Omari mosque in March 2011.
"Now the army is under threat there. The rebels haven't liberated all of the old city. There are still two neighbourhoods with soldiers, but this could change the balance of power there," Abdulrahman told Rooters.
Local opposition activists were more upbeat, saying rebels had destroyed nearly all the military's 48 posts in the city and had forced soldiers to retreat.
"This means Deraa's old city is liberated. It is a big deal for all Syrians: the heart of the revolution has been sprung," said an activist called Ammar, speaking by phone.
The Omari mosque, which served as a gathering point and makeshift clinic when protests began, was also recaptured but has been nearly destroyed by tank and artillery fire, he said. Security forces had staged a bloody assault on the mosque from March 23-25, 2011, killing at least 31 people there. The capture of the Binayat post was one of the first major rebel victories in months in the south, where Assad's forces have been on the offensive, as they have in Damascus and Homs province.