Syrian rebels said on Sunday that they have ended Bashar al-Assad's 24-year authoritarian rule, in their first announcement on state television following a lightning offensive that took the world by surprise.

Syria's army command notified officers on Sunday that Assad's regime had ended, a Syrian officer who was informed of the move told Reuters.

But the Syrian army later said it was continuing operations against "terrorist groups" in the key cities of Hama and Homs and in Deraa countryside.

Assad, who had crushed all forms of dissent, flew out of Damascus for an unknown destination earlier on Sunday, two senior army officers told Reuters, as rebels said they had entered the capital with no sign of army deployments.

"We celebrate with the Syrian people the news of freeing our prisoners and releasing their chains and announcing the end of the era of injustice in Sednaya prison," the rebels said, referring to a large military prison on the outskirts of Damascus where the Syrian government detained thousands.

Thousands in cars and on foot congregated at a main square in Damascus waving and chanting "Freedom" from a half century of Assad family rule, witnesses said.

The dramatic collapse marks a seismic moment for the Middle East, ending the family's iron-fisted rule over Syria and dealing a massive blow to Russia and Iran, which have lost a key ally at the heart of the region.

The pace of events has stunned Arab capitals and raised fears of a new wave of regional instability.

It marks a turning point for Syria, shattered by more than 13 years of war which has turned cities to rubble, killed hundreds of thousands of people, and forced millions abroad as refugees.

Stabilising western areas of Syria captured in the rebels' advance will be key. Western governments, which have shunned the Assad-led state for years, must decide how to deal with a new administration in which a globally designated terrorist group - Hayat Tahrir al-Sham (HTS) - looks set to have influence.

HTS, which spearheaded the rebel advances across western Syria, was formerly an al Qaeda affiliate known as the Nusra Front until its leader Abu Mohammed al-Golani, severed ties with the global jihadist movement in 2016.

"The real question is how orderly will this transition be, and it seems quite clear that Golani is very eager for it to be an orderly one," said Joshua Landis, a Syria expert and Director of the Center for Middle East Studies at the University of Oklahoma.

Golani will not want a repeat of the chaos that swept Iraq after U.S.-led forces toppled Saddam Hussein in 2003. "They are going to have to rebuild ... they will need Europe and the U.S. to lift sanctions," Landis said.

HTS is Syria's strongest rebel group and some Syrians remain fearful it will impose draconian Islamist rule or instigate reprisals.

A Syrian Air plane took off from Damascus airport around the time the capital was reported to have been taken by rebels, according to data from the Flightradar website.

Item 1 of 10 Rebel fighters gather in Homs after Syria's army command notified officers on Sunday that President Bashar al-Assad's 24-year authoritarian rule has ended, a Syrian officer who was informed of the move told Reuters, following a rapid rebel offensive that took the world by surprise, in Homs, Syria December 8, 2024. REUTERS/Mahmoud Hasano

The aircraft initially flew towards Syria's coastal region, a stronghold of Assad's Alawite sect, but then made an abrupt U-turn and flew in the opposite direction for a few minutes before disappearing off the map.

Reuters could not immediately ascertain who was on board.

Two Syrian sources said there was a very high probability that Assad may have been killed in a plane crash as it was a mystery why the plane took a surprise U turn and disappeared off the map according to data from the Flightradar website.

"It disappeared off the radar, possibly the transponder was switched off, but I believe the bigger probability is that the aircraft was taken down...," said one Syrian source without elaborating.

As Syrians expressed joy, Prime Minister Mohammad Ghazi al-Jalali said he was ready to support the continuity of governance and prepared to cooperate with any leadership chosen by the Syrian people.

U.S. President Joe Biden and his team were monitoring the "extraordinary events in Syria" and were in touch with regional partners, the White House said.

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.

The frontlines of Syria's complex civil war were dormant for years. Then Islamists once affiliated with Al Qaeda suddenly burst into action, posing the biggest challenge to Assad, who had survived years of gruelling war and international isolation with the help of Russia, Iran and Lebanon's Hezbollah.

But Assad's allies were focussed on and weakened by other crises, leaving Assad at the mercy of his opponents with an army that was not prepared to defend him.

Israel, which has severely weakened the Iran-backed groups Hezbollah in Lebanon and Hamas in Gaza, will likely celebrate the fall of Assad, another of Iran's key regional allies. But the prospects of an Islamist group ruling Syria will likely raise concerns.

Thousands of Homs residents poured onto the streets after the army withdrew from the central city, dancing and chanting "Assad is gone, Homs is free" and "Long live Syria and down with Bashar al-Assad".

Rebels fired into the air in celebration, and youths tore down posters of the Syrian president, whose territorial control has collapsed in a dizzying week-long retreat by the military.

The fall of Homs gave the insurgents control over Syria's strategic heartland and a key highway crossroads, severing Damascus from the coastal region that is the stronghold of Assad's Alawite sect and where his Russian allies have a naval base and air base.

Homs' capture is also a powerful symbol of the rebel movement's dramatic comeback. Swathes of Homs were destroyed by gruelling siege warfare between the rebels and the army years ago. The fighting ground down the insurgents, who were forced out.

Rebels freed thousands of detainees from the city prison. Security forces left in haste after burning their documents.

The head of Kurdish-led Syrian Democratic Forces Mazloum Abdi said on Sunday on X: “We are witnessing historic moments in Syria as the authoritarian regime in Damascus falls. This change presents an opportunity to build a new Syria founded on democracy and justice, ensuring the rights of all Syrians.”