Around 100 Syrian soldiers and 80 Islamist fighters were killed during a two-day battle in which insurgents captured the Wadi al-Deif military base, the Syrian Observatory for Human Rights monitoring group said on Tuesday.

The Britain-based group said Islamist insurgents including al-Qaida's Syria wing, the Nusra Front, on Monday took the base next to the country's main north-south highway linking Aleppo with Damascus. Fighters also captured the smaller Hamidiya base, southwest of the Wadi al-Deif, the Observatory said.

The group said that around 120 soldiers were captured in the assault, citing insurgent sources.

Forces loyal to President Bashar al-Assad had previously managed to repel numerous attacks on Wadi al-Deif in Idlib province, which has been surrounded by insurgents for two years.

Reuters could not immediately verify the report by the Observatory, which says it tracks the conflict through a network of sources on both sides.

Syrian government officials were not available for comment. Syria's state news agency SANA said that the army had killed several "terrorists" in Idlib province.

SANA also said on Tuesday that the army had killed more than 60 "terrorists" from the Islamic State militant group in the province of Deir al-Zor, hundreds of kilometers (miles) east of Idlib.

Syria's war started with a pro-democracy movement that grew into an armed uprising and has inflamed regional confrontations. Some 200,000 people have died in the conflict, according to United Nations estimates.