Turkey-backed rebels promise reinforcements as Syrian regime troops near key opposition-held village

A Turkey-backed rebel group is to send reinforcements as Syrian regime forces close in on the last remaining opposition bastion in Syria.

Forces loyal to Syrian President Bashar al-Assad captured a string of rebel-held villages in northwest Syria on Thursday, inching closer to Khan Sheikhoun, a key opposition-held town in the embattled Idlib province, a war monitor said.

The National Army and National Liberation Front - two rebel groups supported by Turkey - have joined forces in a bid to hold off the advance.

The National Army, which normally operates out of its strongholds in Aleppo province close to the Turkish border, said on Thursday it would send more fighters to the frontlines to ward off regime fighters, according to Reuters.

The Syrian regime, along with its Russian ally, has led a devastating offensive on the Idlib and Hama provinces since late April in an attempt to win back some of the last remaining rebel-held areas after eight years of brutal civil war.

The regime's fighters have slowly advanced, retaking towns in northern Hama and the southern edges of Idlib controlled by Hayat Tahrir al-Sham (HTS), an extremist group formerly affiliated with Al-Qaeda that controls most of the area.

Although Russia and the regime's airstrikes ostensibly target the extremist militants, civilians have borne the brunt of the ongoing bombardment, with more than 420 civilians killed, according to the Syrian Observatory for Human Rights (SOHR), and around 400,000 displaced, according to the United Nations. 

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Pro-regime troops stood just three kilometres (1.8 miles) from the key town of Khan Sheikhoun on Thursday after capturing five villages to the northwest overnight, the SOHR said.

The town lies on a key highway coveted by the regime, connecting the regime-held capital Damascus with the northern city of Aleppo, which was retaken by forces loyal to Assad in December 2016.

"The aim of the advance is to surround Khan Sheikhun and reach the highway," SOHR head Rami Abdul Rahman told AFP.

But the regime winning back Khan Sheikhoun would also be a powerful symbolic loss for Syrian revolutionaries.

The town was in April 2017 the victim of a deadly chemical attack that killed at least 89 people. The gas attack was committed by the regime, according to the OPCW-UN Joint Investigative Mechanism into the use of chemical weapons in Syria, as well as the governments of the United States, United Kingdom, Turkey and France, among others.

Fighting in Idlib on Thursday killed 20 regime combatants and 24 rebels, according to the Britain-based SOHR.

Regime airstrikes also killed one civilian in southern Idlib, it said. Aerial bombardment on Wednesday claimed at least nine civilian lives.

A day earlier, HTS militants downed a regime plane near Khan Sheikhoun and took the pilot prisoner.

Syria's conflict has killed more than 370,000 people and displaced millions at home and abroad 2011.