Syrian rebels pressed their lightning advance on Saturday, saying they had seized most of the south, as government forces dug in to defend the key central city of Homs to try to save President Bashar al-Assad's 24-year rule.

Since the rebels' sweep into Aleppo a week ago, government defences have crumbled across the country at dizzying speed as insurgents seized a string of major cities and rose up in places where the rebellion had long seemed over.

Besides capturing Aleppo in the north, Hama in the centre and Deir al-Zor in the east, rebels said they have taken southern Quneitra, Deraa and Suweida im the south and advanced to within 50 kilometres of the capital.

Videos on social media released on Saturday showed rebels celebrating, firing in the air, and toppling a statue of former Syrian president Hafez al-Assad in Deraa, the fourth city Assad's forces lost in a week, highlighting growing rebel momentum.

Government defences were focused on Homs, with state television and Syrian military sources reporting big airstrikes on rebel positions and a wave of reinforcements arriving to dig in around the city.

Meanwhile, the rebels extended their control to almost the entire southwest and said they had captured Sanamayn on the main highway from Damascus to Jordan. The Syrian military said it was repositioning, without acknowledging territorial losses.

The pace of events has stunned Arab capitals and raised fears of a new wave of regional instability, with Qatar saying on Saturday it threatened Syria's territorial integrity.

Syria's civil war, which erupted in 2011 as an uprising against Assad's rule, dragged in big outside powers, created space for jihadist militants to plot attacks around the world and sent millions of refugees into neighbouring states.

WATCH | Syrian rebels push on toward Damascus: 

Syrian rebels push on toward Damascus with Turkey’s blessing

Thousands have fled the Syrian city of Homs as Islamist HTS fighters continue their lightning advance toward Damascus, with the apparent blessing of neighbouring Turkey’s president Recep Tayyip Erdogan, who wished them well.

Western officials say the Syrian military is in a difficult situation, unable to halt rebel gains and forced into retreat.

Assad had long relied on allies to subdue the rebels, with bombing by Russian warplanes while Iran sent allied forces including Lebanon's Hezbollah and Iraqi militia to bolster the Syrian military and storm insurgent strongholds.

But Russia has been focused on the war in Ukraine since 2022 and Hezbollah has suffered big losses in its own grueling war with Israel, significantly limiting its ability or that of Iran to bolster Assad.

Russia promises to stop 'terrorists'

Russian Foreign Minister Sergei Lavrov said Moscow was doing all it could to stop "terrorists" prevailing in Syria, and called for dialogue between the Damascus government and the legitimate opposition, without saying which groups this included.

Russia has a naval base and airbase in Syria that have not only been important for its support of Assad, but also for its ability to project influence in the Mediterranean and Africa.

Hezbollah sent some "supervising forces" to Homs on Friday but any significant deployment would risk exposure to Israeli airstrikes, Western officials said. Israel attacked two Lebanon-Syria border crossings on Friday, Lebanon said.

Iran-backed Iraqi militias are on high alert, with thousands of heavily armed fighters ready to deploy to Syria, many of them amassed near the border. Iraq does not seek military intervention in Syria, a government spokesperson said on Friday.

Iran, Russia, and Turkey, which is the rebels' main foreign supporter, discussed the crisis in Doha. Lavrov said they had agreed there should be an immediate end to the fighting.

A top Iranian official, Ali Larijani, met Assad in Damascus on Friday, an Iranian news agency reported a lawmaker as saying. Iranian Foreign Minister Abbas Araqchi said "no specific decisions have been made regarding a horizon for Syria's future."

Battle for Homs includes airstrikes

The rebels said they were "at the walls" of Homs after taking the last village on its northern outskirts late on Friday.

Inside Homs, a resident said the situation had felt normal until Friday but had grown more tense with airstrikes and gunfire clearly audible and pro-Assad militia groups setting up checkpoints.

"They are sending a message to people to keep in line and that they should not get excited and not expect Homs to go easily," the resident said.

WATCH | Civilians at risk as Syria violence flares, UN chief says: 

Civilians at risk as Syria violence flares, UN chief says

United Nations Secretary General António Guterres says after years of conflict in Syria, it is 'high time' for all parties to engage seriously and chart a path to resolving the long-running crisis.

Seizing Homs, an important crossroads between the capital and the Mediterranean, would cut off Damascus from the coastal stronghold of Assad's minority Alawite sect, and from a naval base and airbase of his Russian allies there.

A Syrian military officer said there was a lull in fighting on Saturday morning after a night of intense airstrikes on the rebels and that a large convoy of troops and vehicles had redeployed from Palmyra to aid the Homs defense.

A coalition of rebel factions that include the Islamist group Hayat Tahrir al-Sham made a last call on forces loyal to Assad's government in Homs to defect.

"Homs is the key. It will be very hard for Assad to make a stand but if Homs should fall, the main highway from Damascus to Tartus and the coast will be closed, cutting the capital off from the Alawite Mountains," said Jonathan Landis, a Syria specialist at the University of Oklahoma.

In the south, the fall of Deraa and Suweida on Friday, followed by Quneitra on Saturday, could allow a concerted assault on the capital, the seat of Assad's power, military sources said.

Deraa, which had a population of more than 100,000 before the civil war began, holds symbolic importance as the cradle of the uprising. It is the capital of a province of about one million people, bordering Jordan.

In the east, a U.S.-backed alliance led by Syrian Kurdish fighters captured Deir el-Zor, the government's main foothold in the vast desert, on Friday, three Syrian sources told Reuters, jeopardizing Assad's land connection to allies in Iraq.