Its forces are now close to the military air base of Abu Duhur, their next target, the war monitor said.
Later, they fired rockets at regime positions from farmland in the Al-Tamana area of southern Idlib, an AFP correspondent said.
Turkey and NGOs have warned of a new humanitarian disaster in Syria with the regime offensive on Idlib, the last province in rebel hands.
The Observatory said Thursday that 96 civilians have been killed since the military campaign on Idlib and Hama countrysides started on Dec.25.
Since losing the airbase in 2015 following a two-year jihadist siege, the Syrian government has only had control of two villages in Idlib province: Fua and Kafraya. The attack also aims to secure the road liking the capital, Damascus, with the northern city of Aleppo, Syria's largest.
Almost 100,000 people have been displaced since early December by fighting in northwestern Syria, where the regime is waging an offensive against jihadis, the United Nations said on Wednesday.
The International Rescue Committee said it had received hundreds of people newly displaced from the latest fighting in Idlib, many of them housed in makeshift tents.
At least 11 civilians were killed in heavy Syrian regime air raids on Idlib province on Friday night, where fighting on the ground has raged for over a week.
Lowcock said he was "deeply anxious about civilians affected by the upsurge in violence in Idlib".
"The operation is to hit the belly of the regime deep into liberated territories and to encircle their advancing forces", said Abdul Hakim al Rahamon, a senior official in Jaish al Nasr, an FSA faction taking part.
Syria's war began in 2011, when an armed uprising against Bashar al-Assad's regime erupted as anti-government protests were brutally crushed.
Andy Murray looks to sport management role for future talent
He says that he still wishes to compete in professional tennis but he also wants to expand his prospects and share his knowledge. At the moment he is juggling many balls and he wants to remain focused on what he knows, but over time his company will develop.
Smart home security needs to be a priority reveals Mirai.
This is why they are able to potentially cause so much harm, and why they are such a possibly lucrative target for attacks. Manufacturers are also focussed on keeping costs down in order to attract consumers, and security is not cheap.