Al Qaeda's affiliate in Syria Monday took control of a government military base in the northern province of Idleb, the Syrian Observatory for Human Rights (SOHR) said.
With support from another radical group, the Nusra Front captured the Wadi al-Diff base and nearby areas in the city of Maret Nuaman, the London-based monitoring organisation said.
The fighters began attacking the base Sunday using anti-tank missiles. In the battle, at least 15 Syrian soldiers and eight Islamists died, SOHR said.
In its report on the fighting, the Syrian government news agency SANA, said the Syrian armed forces killed several "terrorists" in the suburbs of Maret Nuaman, without providing further details.
Wadi al-Diff is located to the east of Maret Nuaman and is next to a major north-south highway which connects the capital Damascus with Aleppo.
Controlling this vital transport link would enable the rebels to threaten the regime's main supply lines to Aleppo.
More than 200,000 people have died since a number of rebel groups took up arms against the Syrian government in 2011 as the so-called Arab Spring swept the Middle East.