The attempted southern advance on Sunday comes on the fifth day of the surprise rebel offensive as Syrian and Russian forces have launched counterattacks, reportedly pounding opposition-controlled Idlib province and Aleppo with air attacks since Saturday.

Government forces under the control of Syrian President Bashar al-Assad have also been fortifying the northern province of Hama, according to the Syrian state news agency, SANA.  It reported the army overnight pushed back opposition fighters in its northern countryside. Forces there were being resupplied with heavy equipment and rocket launchers, according to SANA.

On Sunday, United Nations special envoy to Syria, Geir Pedersen, appealed for all stakeholders in the conflict to immediately seek a political resolution.

“The latest developments pose severe risks to civilians and have serious implications for regional and international peace and security,” he said.

The fighting marks the most significant turn in years in the Syrian war, which began with popular uprisings across the country in 2011.

Since 2020, the front lines had largely been stagnant with an array of rebel groups largely contained to a small portion of Idlib province.

But on Friday, opposition fighters led by Hayat Tahrir al-Sham (HTS) entered Aleppo, prompting government forces to withdraw from the strategically significant city of more than 2 million people.

The rebels have since claimed several strategic victories, including taking control of the supply-line town of Khansir, Aleppo Industrial City, Aleppo’s military academy and the field artillery college.

Formerly known as al-Nusra Front, the Syrian branch of al-Qaeda, HTS has distanced itself from the group while becoming the strongest opposition movement in northwestern Syria.

It is still considered a “terrorist” organisation by the United States, Syria and Russia.

In his first public comments since the start of the offensive, released late on Saturday, al-Assad said his forces will continue to defend the government’s “stability and territorial integrity against terrorists and their supporters”.

He said Syria is able to defeat the rebel groups no matter how much their attacks intensify.

The government said air strikes on opposition-controlled areas were targeting weapon depots and rebel strongholds.

However, the United Kingdom-based war monitor, the Syrian Observatory for Human Rights, said Russian strikes hit camps for displaced people on Sunday, killing eight civilians and wounding 50.

The Syrian Civil Defence, which operates in opposition-held areas, also reported a series of attacks on Aleppo, including the Aleppo University Hospital in the centre of the city. It was not immediately clear if there were any casualties.

Years of war in Syria have created one of the world’s largest displacement crises with thousands more people reported displaced in the latest fighting.

Razan Saffour, a British-Syrian human rights activist with family in Aleppo, said that while there is relative stability in Aleppo, there is fear over the response from government and Russian forces.

Russia’s military intervention in the country starting in 2015 as well as Iran’s two years earlier helped to turn the tide of the war in favour of al-Assad. Russia’s aerial bombardments of Aleppo then helped government forces take full control of the city in 2016.

“We’re speaking about rebel groups who are gaining Syrian territory at a very, very fast pace, but at the same time, they don’t have air defences,” she said.

“And when we’ve seen this happen [previously], … the al-Assad regime, Russia and their ally Iran responded with a scorched earth policy.”

Iranian Foreign Minister Abbas Araghchi was to travel to Damascus on Sunday, telling reporters Tehran would back al-Assad.

Jordan’s King Abdullah II and United Arab Emirates President Sheikh Mohamed bin Zayed Al Nahyan also expressed solidarity with al-Assad in recent calls with him.

Still, Saffour said that beyond the confusion and fear, there is also a sense of anticipation among some residents of Aleppo who had lived for years under government control.

“We’re very apprehensive, but we’re also very excited and very hopeful to see what’s going to come next,” she said.

Russia launched air strikes in response across parts of Aleppo overnight into Saturday for the first time since 2016, the observers added.

SOHR said more than 300 people – including more than 20 civilians – have been killed since the offensive started on Wednesday.

The offensive is the largest against the Syrian government in years and the first time rebels fighting the forces of President Bashar al-Assad have reached Aleppo since being forced out by the army in 2016.

Syria’s military confirmed on Saturday that rebels had entered “large parts” of the city and dozens of soldiers had been killed or injured in the fighting.

In a statement, it said troops had been withdrawn from Aleppo temporarily “to prepare a counteroffensive”.

Aleppo’s airport and all roads leading into the city have been closed, military sources told Reuters news agency.

The rebels were able to capture the “majority of the city” without meeting significant resistance, the SOHR said early on Saturday.

There was “no fighting” as Syrian regime forces withdrew, a spokesperson said.

“The city council, police stations, intelligence offices – they are empty.”This has never happened before”.

Earlier on Friday, government forces said they had regained positions in a number of towns in Aleppo and Idlib provinces, following the offensive launched by HTS and allied factions on Wednesday.

Video posted on a channel affiliated with the Islamist militant group Hayat Tahrir al-Sham (HTS) appears to show rebel fighters in vehicles inside the city.

AFP said one of its reporters had seen “anti-government fighters” in front of the city’s landmark citadel on Friday.

More than half a million people have been killed in the civil war that erupted after the government cracked down on pro-democracy protests in 2011.

An array of armed groups opposed to the Assad government – including jihadists – took advantage of the turmoil to seize swathes of territory.

The Syrian government – with help from Russia and other allies – later retook most the areas it had lost.

Idlib, the last remaining opposition stronghold, is mostly controlled by HTS, but Turkish-backed rebel factions and Turkish forces are also based there.

Syrian and Russian planes carried out 23 air strikes near Idlib on Friday, according to SOHR.

The UK-based monitoring group, which uses a network of sources on the ground in Syria, said four civilians were killed and 19 others were injured in the Russian strikes.

Russia’s military said it had bombed “extremist forces”, according to Russian news agencies.

Kremlin spokesman Dmitry Peskov expressed his support for “the government of Syria to quickly restore order” and said the country’s sovereignty was under attack.

The UN’s deputy regional humanitarian co-ordinator for Syria, David Carden, said he was deeply alarmed by the impact of the escalating hostilities on civilians.

“Relentless attacks over the past three days have claimed the lives of at least 27 civilians, including children as young as eight years old”, he said.

Fighting in Idlib had largely wound down since 2020, when Turkey and Russia, Syria’s key ally, brokered a ceasefire to halt a push by the government to retake the province.

But on Wednesday HTS and its allies said they had launched their offensive to “deter aggression”, accusing the government and allied militias of escalation in the region.

Analysts say one reason they advanced so quickly is because Syria’s allies, Iran and Hezbollah, have been weakened by Israeli attacks in the region.

The UK-based group says fighters set off two car bombs before advancing into neighbourhoods, without giving further details.

Government forces meanwhile say they have regained control of positions that had been taken by rebels in the Idlib and Aleppo countryside, Syria’s state news agency reported.

The Islamist militant group Hayat Tahrir al-Sham (HTS) and allied factions said they seized a number of towns and villages in Aleppo and Idlib provinces after launching the offensive on Wednesday.

The monitoring group Syrian Observatory for Human Rights (SOHR), which uses a network of sources on the ground in Syria, reported that Syrian and Russian planes carried out 23 air strikes on Aleppo city and the surrounding countryside on Friday.

The SOHR said 255 people, mostly combatants, had been killed in the fighting, the deadliest between rebels and pro-government forces in Syria for years.

It said opposition forces had taken control of more than 50 towns and villages since Wednesday.

Fighting which had raged since the civil war began in Syria in 2011 had largely wound down by 2020, when Turkey and Russia – Syria’s key ally – brokered a ceasefire to halt a push by the government to retake Idlib.

That led to an extended lull in violence, but sporadic clashes, air strikes and shelling continued.

Idlib is the last remaining opposition stronghold and is home to more than four million people, many of whom have been displaced during the conflict and are living in dire conditions.