- Rebels enter suburbs of city of Homs, sources say
- Insurgents seize almost entire southwest in 24 hours
- Protesters topple Damascus statue to Assad's father
Since the rebels' sweep into Aleppo a week ago, government defences have crumbled at dizzying speed as insurgents seized a string of major cities and rose up in places where the rebellion had long seemed over.
The twin threats to strategically vital Homs and the capital Damascus now pose an existential threat to Assad's decades of rule in Syria.
A Homs resident, and army and rebel sources said the insurgents had breached government defences from the north and east of the city. A rebel commander said they had taken control of an army camp and villages outside the city.
State television reported that the insurgents had not penetrated into Homs although it said they were on the city outskirts, where it said the military was striking them with artillery and drones.
Insurgents have seized almost the entire southwest within 24 hours, and they have advanced to within 30 km (20 miles) of Damascus as government forces fell back, rebels said.
Underscoring the possibility of an uprising in the capital, protesters in a Damascus suburb tore down a statue of Assad's father and ripped it to pieces. In other suburbs soldiers changed into civilian clothes and deserted their posts, residents said.
Assad remains in Damascus, Syria's state news agency said.
The pace of events has stunned Arab capitals and raised fears of a new wave of regional instability.
US President-elect Donald Trump said the US should not be involved in the conflict and should "let it play out".
The foreign ministers of Russia, Iran and the main rebels' backer Turkey met on Saturday and agreed on the importance of Syria's territorial integrity and on restarting a political process, they said.
But there was no indication they agreed on any concrete steps, with the situation inside Syria changing by the hour.
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.
Iran has said it would consider sending forces to Syria, but any immediate extra assistance would likely depend on Hezbollah and Iraqi groups.
The Lebanese group sent some "supervising forces" to Homs on Friday but any significant deployment would risk exposure to Israeli airstrikes, Western officials 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 spokesman said on Friday.
Britain warned Assad that any chemical weapons use was a red line and would be met with "appropriate action".
The Homs resident said he had seen the rebels advance past a Syrian Air Force base in the north of the city that was considered a major defensive area. The resident later said fighting was audible in the city outskirts.
An opposition figure in touch with rebel command and a Syrian army source both also said the insurgents were inside the city.
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 Russia's air and naval base.
In the south, the rapid collapse of government control could allow a concerted assault on the capital, the seat of Assad's power.
The Syrian military pulled back as far as Saasa 30 km from Damascus to regroup, a Syrian army officer said.
Jarmana, where protesters pulled down a statue of Hafez al-Assad, the current president's father, is in the city's southern suburbs. Soldiers were deserting in the former rebel stronghold of Daraya and in Mezzeh, near a major airbase, residents said.
The main rebel group, the Islamist Hayat Tahrir al-Sham, said it had a duty to protect governmental, international and UN offices in Syria.
In a sign of government forces' collapse in the east, around 2,000 Syrian soldiers crossed the border into Iraq to seek sanctuary, the mayor of Iraqi border town al-Qaem said.
Syrian Kurdish fighters had captured eastern Deir el-Zor on Friday, jeopardising Assad's land connection to allies in Iraq.