Crowds gathered in Damascus on Sunday to celebrate with chants, prayers and the occasional gunfire after the stunning advance from opposition forces put an end to the Assad family's 50 years of iron rule but raised questions about the future of the country and the wider region.

President Bashar Assad and other officials left Syria, after resigning and hosting negotiations with rebel groups, Russia's Foreign Ministry claimed Sunday. Hours later, Russian state media news agencies reported that Assad and his family were in Moscow and given asylum.

The agencies, Tass and RIA, cited an unidentified Kremlin source. CBS News could not immediately verify the reports.

In a post on the Telegram messaging app on Sunday, the ministry said Assad left Syria after negotiations with opposition fighters and gave "instructions" to "transfer power peacefully."

"Russia did not participate in these negotiations," the ministry said, adding that it has been following the "dramatic events" in Syria "with extreme concern."

It was the first time opposition forces had reached Damascus since 2018 when Syrian troops recaptured areas on the outskirts of the capital following a yearslong siege.

President Biden, who met with his national security team Sunday morning to discuss the latest developments in Syria, called the fall of Syrian leader Assad a "moment of history of opportunity," pledging to support the country and its neighbors against any threats.

"At long last, the Assad regime has fallen," Biden said at the White House Sunday afternoon, hours after opposition forces took over the country.

Celebrations in the capital

The leader of the largest insurgent group in Syria visited the Syrian capital's sprawling Umayyad Mosque and declared that the victory against Assad "is a victory to the Islamic nation."

Ahmad al-Sharaa, who was formerly known as Abu Mohammed al-Golani, made his first public appearance and remarks since fighters entered Damascus. He told hundreds of people at the historic mosque that Assad had made Syria "a farm for Iran's greed." He added that Assad made Syria a base for the illegal amphetamine Captagon that brought cash to Assad's circles.

Videos from Damascus showed families wandering into the presidential palace, with some emerging carrying stacks of plates and other household items.

"I did not sleep last night, and I refused to sleep until I heard the news of his fall," said Mohammed Amer Al-Oulabi, 44, who works in the electricity sector. "From Idlib to Damascus, it only took them (the opposition forces) a few days, thank God. May God bless them, the heroic lions who made us proud."

The rapidly developing events have shaken the region. Lebanon said it was closing its land border crossings with Syria except for one that links Beirut with Damascus. Jordan also closed a border crossing with Syria.

The rebels now face the daunting task of healing bitter divides in a country ravaged by war and still split among different armed factions. Turkey-backed opposition fighters are battling U.S.-allied Kurdish forces in the north, and the Islamic State group is still active in some remote areas.

Syrian state television aired a video statement early Sunday by a group of rebels saying that Assad had been overthrown and all prisoners had been set free. The man who read the statement called on rebel fighters and citizens to preserve the institutions of "the free Syrian state."

Reaction from around the world

Iran, which had strongly backed Assad's deposed government, says Syrians should decide their country's future "without destructive, coercive, foreign intervention."

The Gulf nation of Qatar, a key regional mediator, hosted an emergency meeting of foreign ministers and top officials from eight countries with interests in Syria late Saturday. The participants included Iran, Saudi Arabia, Russia and Turkey.

The French Foreign Affairs ministry said France "welcomes" the fall of Assad's government "after more than 13 years of violent repression against its own people."

The ministry said in a statement: "The Syrian people have suffered too much. Bashar Assad has bled dry country, emptied of a large part of its people who, if not forced into exile, have been massacred, tortured and bombarded with chemical weapons by the regime and its allies."

German Foreign Minister Annalena Baerbock expressed understanding for the relief Syrian people felt after the fall of Assad's government but warned that "the country must not now fall into the hands of other radicals."

"Several hundred thousand Syrians have been killed in the civil war, millions have fled," Baerbock said in a statement emailed by her office Sunday. "Assad has murdered, tortured and used poison gas against his own people. He must finally be held accountable for this."

Germany has the largest Syrian diaspora in the European Union, more than 1 million strong. Thousands of jubilant Syrians gathered in Berlin on Sunday to celebrate the fall of Assad, sounding car horns and waving Syrian opposition flags, AFP reported.

"We're happy. The dictatorship is over. Assad has gone," 39-year-old Ahmed, who preferred not to give his last name, told AFP.

"All Syrians are together now," said the railway technician, who fled the northern Syrian city of Aleppo in 2015.

The war in Syria began in 2011 when a pro-democracy uprising calling for the end of Assad's long reign escalated quickly into a brutal civil war. Since then, the conflict has killed more than 500,000 people and displaced some 12 million from their homes.

Margaret Brennan contributed to this report.