BEIRUT (AP) — Turkey-backed Syrian opposition fighters Thursday retook a strategic northwestern town in Syria, opposition activists said, and cut off the key highway linking the capital, Damascus, with the northern city of Aleppo, days after the government reopened it for the first time since 2012.

Despite the loss of Saraqeb, government forces made major gains to the south, taking control of almost the entire southern part of Idlib province with the capture of more than 20 villages Thursday, state media and opposition activists said.

The retaking of Saraqeb, which sits on the M5 highway, is a setback for Syrian President Bashar Assad's forces who have scored major gains in a weekslong Russian-backed campaign in the last rebel stronghold in Idlib province. Officials had hailed the reopening of the motorway as a major victory in the nine-year conflict.

The government's military campaign to recapture Idlib, the last opposition-held stronghold in the country, has triggered a humanitarian catastrophe and the war's largest single wave of displacement. According to the U.N., almost 950,000 civilians have been displaced since early December, and more than 300 have been killed. Most have fled farther north to safer areas near the Turkish border, overwhelming camps already crowded with refugees in cold winter weather.

The Britain-based Syrian Observatory for Human Rights, an opposition war monitoring group, said the opposition fighters seized the town of Saraqeb after intense bombardment by Turkish troops. Turkey and Russia support opposite sides in Syria's brutal civil war, with Ankara backing the opposition and Moscow backing Assad.

From inside Saraqeb, activist Taher al-Omar said the town is now under opposition control. He posted a video with a fighter saying the government forces “ran away like rats.”

The Observatory said more than 60 fighters were killed on both sides since Wednesday, adding that later on Thursday, government forces launched a counteroffensive under the cover of Russian airstrikes to try retake the town.

Syrian state media reported intense clashes near Saraqeb, saying insurgents sent suicide car bombs and that Turkish forces bombarded the area. It said a small group of insurgents reached the highway to score a “propaganda stunt,” adding that “Syrian troops are dealing with them.”

State TV later Thursday confirmed that insurgents have cut the highway adding the fighting is ongoing in the area.

In southern parts of Idlib, government forces captured more than 20 villages since late Wednesday bringing southern parts of the rebel stronghold under government control, the Observatory said. It added that Syrian troops have now besieged another Turkish observation post in an area known as Sheer Maghar, it added.

The government controlled Syrian Central Military Media said government forces marching from northern parts of Hama province met Thursday with forces moving from southern Idlib bringing wide areas under Syrian army control.

If government forces now turn their march north they can eventually reach another major highway known as the M4 that links Syria's coastal region with the country's west. Assad has vowed to regain control of all parts of Syria.

Backed by Russian air power, Assad's forces have over the past few days captured dozens of villages, including major rebel strongholds, in the last opposition-held area.

The campaign also seized the last segments of the south-north M5 highway. When the government forces first took Saraqeb earlier this month, it marked their capture of the last major rebel-held town along the highway.

In recent weeks, Turkey has sent thousands of troops into Idlib. Clashes between Syrian and Turkish troops have killed 18 Turkish soldiers.

Turkey's Defense Ministry said Thursday two Turkish soldiers were killed in Syria in an air attack in the province the previous day, and that two others were wounded.

Turkey responded by targeting Syrian government forces. An air defense missile system, an anti-aircraft gun, three tanks, an ammunition vehicle, an anti-tank weapon and two construction vehicles were destroyed, the ministry said.

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Associated Press writers Andrew Wilks in Ankara, Turkey, and Albert Aji in Damascus, Syria, contributed to this report.