After recapturing most of Syria, President Bashar al-Assad is threatening to march on opposition forces in Idlib, the densely populated northwest province that shares a border with rebel ally Turkey.
But a military assault would prove very costly, and analysts say Ankara and regime ally Moscow may ultimately choose to keep Assad's troops in check.
- The last redoubt -
Idlib is the last haven for Syria's fractured armed opposition, which this year alone lost key bastions near Damascus and in the south.
The province shares a roughly 100-kilometre (60-mile) border with Turkey and fell to jihadists and rebels in 2015.
Now, around 60 percent is held by Hayat Tahrir al-Sham (HTS), led by jihadists from Al-Qaeda's former Syria affiliate.
The rest is controlled by rival Islamists and rebels, while regime forces hold a southeastern sliver.
The province forms a "de-escalation zone" agreed in 2017 by Turkey, Russia, and fellow regime ally Iran meant to prevent hostilities there.
It is the only such zone left, after Assad recaptured the other three this year.
- Why does Assad want Idlib? -
Throughout Syria's seven-year war, Assad has pledged to recapture every inch of the country. After Turkish troops intervened in 2016, Damascus regularly lambasted them as "occupiers".
Last week, Assad said Idlib, where Turkey has forces deployed, is his next priority.
Idlib's strategic importance for the regime lies at least in part in the M5 highway, which links second city Aleppo in the north to Damascus, and then south to the recently recaptured Nassib border crossing with Jordan.
The stretch in Idlib cuts through rebel territory, but Turkish and Russian monitors are positioned along it.
Assad's push for Idlib will primarily stem from his interest in the highway, says analyst Fabrice Balanche.
- How likely is an assault? -
Talk of a possible looming assault on Idlib is rife in government-held Syria, but analysts say there is cause to be cautious.
First, Russia's own Syria envoy Alexander Lavrentiev said this week there was "no question of an operation" on Idlib.
The regime's main obstacle, says Center for a New American Security analyst Nicholas Heras, is Ankara.
"The greatest impediment to the Assad government in Idlib is Turkey and the Turkish government's policy toward northwest Syria," he says.