Syrian government troops captured a northwestern village known for its medieval fortress on Thursday as they move deeper toward Idlib province, the last major rebel stronghold, activists and pro-government media said.

The latest wave of fighting that began last week is the most serious challenge yet to a cease-fire in the region, brokered by Russia and Turkey in September.

The Britain-based Syrian Observatory for Human Rights, a war-monitoring group, said government forces captured the village of Qalaat al-Madiq after insurgents pulled out. Idlib-based activist Alaa Moadamani confirmed the village’s capture.

The pro-government Syrian Central Military Media said troops took Qalaat al-Madiq and two smaller nearby villages. Government troops had been holding the nearby fortress, which also carries the name of Qalaat al-Madiq.

The village, near the Orontes River, is a gateway to the fertile plain of al-Ghab, a breadbasket for the central province of Hama. The village was built on the site of the ancient city of Apamea and the fortress overlooking it was built during Muslim rule in the 12th century.

Thursday’s push came a day after Syrian troops took the nearby village of Kfar Nabudah- which activists called Idlib’s first line of defense

The latest offensive, which began April 30, has raised fears of a wider government push on Idlib, which is home to about 3 million people, many of them displaced from elsewhere in Syria.

The U.N. says over 150,000 people have been displaced recently within the enclave.

The government appears to be trying to secure access to a major highway that cuts through the rebel-held enclave. The highway was to reopen before the end of 2018, following the cease-fire agreement between Russia and Turkey, but it remains closed.

Rasheed al-Ahmed, a pharmacist from Kfar Nabudah, said all the village’s residents fled to the north, settling in camps along the border with Turkey. He said the government troops, aided by Russian forces, entered the village in droves with aircraft overhead. Neighboring villages were also emptied, he said, amid the fast-moving offensive.

“People are living between trees and in farms,” Al-Ahmed said, adding he secured his family a place in Atmeh near the border. “It is a deplorable situation.” The activist-operated Thiqa news agency filmed a group of civilians living between olive trees where they spread out rugs to sleep and sit on. The civilians hung their few belongings on plastic bags on the tree branches.

Moadamani, the Idlib-based activist, said “people are terrified as more flee their homes,” adding that many who fled were sleeping in their cars.

Meanwhile, the US-backed Syrian Democratic Forces took credit for defeating the Daesh group in its last stronghold in eastern Syria, celebrating the victory in front of throngs of journalists at a ceremony in March following a bloody four-year war.

But the Kurdish-led force now faces protests by local Arab tribesmen in Deir el-Zour province demanding better services, jobs and a bigger role in decision-making in the predominantly Arab, oil-rich and fertile region. Though limited to about a dozen villages for now, the demonstrations are a growing challenge to the US and its local partners at a time when President Donald Trump plans to reduce America’s military presence in Syria.

On Thursday, the Kurdish-led fighters opened fire at protesters in the village of Shheil, killing one person — the first fatality since the protests began last month, according to Syrian state TV and the DeirEzzor24 activist collective, which monitors developments in the province.

The protest came after an overnight raid in the village by the US-led coalition and the Kurdish force killed six people, according to DeirEzzor24 and the Britain-based Syrian Observatory for Human Rights, a war monitoring group. The Observatory said two people, one of them a Daesh member, were arrested.

An SDF official, who spoke on condition of anonymity because he was not authorized to speak to the media, said the protesters so far are a small percentage of Deir el-Zour residents. But the demonstration benefit the Syrian government, its Iranian backers and Turkey, and undermine “our victory against Daesh,” he said.

Several rounds of talks between the SDF and local officials have so far failed to make progress, leading to concerns the protests could transform into an all-out uprising against the predominantly Kurdish force, founded in 2015 to fight Daesh and armed by the US.

Agencies