Syrians awakened on Monday to a hopeful if uncertain future, after rebels seized the capital Damascus and President Bashar al-Assad fled to Russia, following 13 years of civil war and more than 50 years of his family's brutal rule.

The lightning advance of a militia alliance spearheaded by Hayat al-Tahrir al-Sham (HTS), a former al-Qaeda affiliate, marked one of the biggest turning points for the Middle East in generations. Assad's fall wiped out a bastion from which Iran and Russia exercised influence across the Arab world.

Moscow gave asylum to Assad and his family, Russian media reported and Mikhail Ulyanov, Russia's ambassador to international organisations in Vienna, said on his Telegram channel on Sunday.

International governments welcomed the end of the Assads' autocratic government, as they sought to take stock of a new-look Middle East.

U.S. President Joe Biden said Syria is in a period of risk and uncertainty, and it is the first time in years that neither Russia, Iran nor the Hezbollah militant organisation held an influential role there.

HTS is still designated as a terrorist group by the U.S., Turkey and the United Nations, although it has spent years trying to soften its image to reassure international governments and minority groups within Syria.

Assad's overthrow limits Iran's ability to spread weapons to its allies and could cost Russia its Mediterranean naval base. It could also allow millions of refugees scattered for more than a decade in camps across Turkey, Lebanon and Jordan to finally return home.

NOW TO REBUILD

The rebels face a monumental task of rebuilding and running a country after a war that left hundreds of thousands dead, cities pounded to dust and an economy hollowed by global sanctions. Syria will need billions of dollars in aid.

"A new history, my brothers, is being written in the entire region after this great victory," said Ahmed al-Sharaa, better known as Abu Mohammed al-Golani, the head of HTS.

Speaking to a huge crowd on Sunday at Damascus' Umayyad Mosque, a place of enormous religious significance, Golani said with hard work Syria would be "a beacon for the Islamic nation."

Assad's prime minister, Mohammed Jalali, told Sky New Arabia he would be willing to meet with Golani and was ready to provide documents and assistance for the transfer of power. He said he had no answer to the fate of the Syrian army.

"It is a question left to the brothers who will take over the management of the country's affairs, what concerns us today is the continuation of services for Syrians," he said.

The Assad police state was known as one of the harshest in the Middle East with hundreds of thousands of political prisoners held in horrifying conditions.

On Sunday, elated but often confused inmates poured out of jails. Reunited families wept in joy. Newly freed prisoners were filmed running through the Damascus streets holding up their hands to show how many years they had been in prison.

The White Helmets rescue organisation said it had dispatched emergency teams to search for hidden underground cells still believed to hold detainees.

With a curfew declared by the rebels, Damascus was calm after dawn on Monday, with shops closed and streets in the city largely empty.

The majority of people seen were rebels, dressed in fatigues and carrying weapons, while many cars had license plates from the northwestern province of Idlib, where the rebel offensive was launched 12 days ago.

Near downtown, a single bookseller could be seen carefully laying novels out on a ledge.

The rebel coalition said it was working to complete the transfer of power to a transitional governing body with executive powers, referring to building "a Syria together."

Golani is a Sunni Muslim, which is the majority in Syria, but the country is home to a wide range of religious sects, including Christians and Assad's fellow Alawites, an offshoot of Shi'ite Islam.

WORLD STUNNED

The pace of events stunned world capitals and prompted an outpouring of celebrations from Syrian diaspora. In Sydney, people paraded in cars while waving Syrian flags, danced in the streets and set off fireworks.

It also raised concerns about more regional instability on top of the Gaza war, Israel's attacks on Lebanon and tensions between Israel and Iran.

The U.S. Central Command said its forces conducted dozens of airstrikes targeting known Islamic State camps and operatives in central Syria on Sunday.

Secretary of Defense Lloyd Austin said on Sunday he spoke with Turkish Minister of National Defense Yasar Guler, emphasising the importance of protecting civilians and that the United States is watching closely.

During Syria's civil war, which erupted in 2011 as an uprising against Assad, his forces and their Russian allies bombed cities to rubble. The refugee crisis across the Middle East was one of the biggest of modern times and caused a political reckoning in Europe when a million people arrived in 2015.

In recent years, Turkey had backed some rebels in a small redoubt in the northwest and along its border. The United States, which has about 900 troops in Syria, backed a Kurdish-led alliance that fought Islamic State jihadists from 2014-2017.