Government forces pounded the south of Idlib and nearby Hama with air and ground attacks this week, pressing an offensive that has caused a new exodus. The United Nations says the escalation since late April has killed hundreds of people.
The northwest corner is all that remains in the hands of rebel fations who have suffered a string of crushing blows across Syria in the more than eight-year war.
President Bashar al-Assad has turned to the Idlib region after clawing back control of most of Syria with key help from Russia and Iran. Still, the prospect of more advances is obstructed not only by Turkey's interests near its border but also U.S. forces alongside Kurdish fighters in the northeast.
The latest army gains have put Turkish troops in Idlib in the firing line and threaten Ankara's hopes of preventing a new wave of refugees on its border.
The pocket that came under state rule on Friday includes a few towns and their environs which rebels had held since the early years of the conflict.
Rebel officials did not respond to requests for comment.
The army imposed "a choking siege" on insurgents in the Hama countryside on Friday morning, state-run Ikhbariya said.
The capture of six towns and nearby hills expanded state control of a highway running through them, which stretches from the capital Damascus to Aleppo city, it added.
"The north Hama countryside is now fully safe," the channel's correspondent said in a live broadcast from the town of Kfar Zita. He said soldiers were searching for landmines.
The Syrian Observatory for Human Rights said pro-government force recovered Kafr Zita, which insurgents had controlled since 2012, and some towns nearby.
The fate of a Turkish military post in one of the towns which was also encircled, Morek, remained unclear, the UK-based war monitor and state TV said.
Under its deals with Russia, Turkey has forces stationed at a dozen military posts across Idlib. Ankara backs rebel forces that control swathes of territory further north near its border, and some that have a presence in Idlib.Moscow and Damascus say they are responding to militant attacks by the former Nusra Front, a jihadist alliance now known as Hayat Tahrir al-Sham which is the dominant force in Idlib.