Syria's Assad is now in Moscow, Russian state media says

The Russian Foreign Ministry said in a Sunday morning statement that Syrian President Bashar al-Assad "decided to leave the presidential post and left the country, giving instructions to transfer power peacefully."

Assad's whereabouts remain unknown as rebels celebrate the fall of his government in Damascus and across the country. The lightning rebel offensive that began last month proved the final chapter in Assad's more than 24 years in power -- and the end of his family's 50-year rule.

"We are following the dramatic events in Syria with extreme concern," the Russian Foreign Ministry said. Assad stepped down "as a result of negotiations" with "a number of participants in the armed conflict," the statement said.

"Russia did not participate in these negotiations," it added. "At the same time, we appeal to all parties involved with a strong call to renounce the use of violence and resolve all governance issues by political means."

Moscow "is in contact with all groups of the Syrian opposition," the statement said, and supports "efforts to establish an inclusive political process based on the unanimously adopted UN Security Council Resolution 2254."

"All necessary measures are being taken to ensure the safety of our citizens in Syria," the ministry said. "Russian military bases in Syria are on high alert. There is currently no serious threat to their security."

The Iranian embassy in Damascus has been stormed and looted by Syrians celebrating the fall of President Bashar al-Assad's government, which for several years was heavily reliant on Iranian and Russian backing, state-run media in Tehran reported.

Iran's state-owned PressTV said the mission was ransacked by "militants led by Hayat Tahrir al-Sham," one of the rebel groups leading the surprise campaign that toppled the Syrian government.

Videos from the scene showed people tearing down posters outside the embassy that bore images of former Islamic Revolutionary Guard Corps Quds Force commander Qassem Soleimani and former Hezbollah leader Hassan Nasrallah.

The footage also showed people carrying items out of the mission and smashing its windows.

-ABC News' Joe Simonetti

Geir Otto Pedersen, the United Nations' special envoy for Syria, said in a statement Sunday that the fall of President Bashar al-Assad's government "marks a watershed moment" in the country's history after "nearly 14 years of relentless suffering and unspeakable loss."

"This dark chapter has left deep scars, but today we look forward with cautious hope to the opening of a new one -- one of peace, reconciliation, dignity and inclusion for all Syrians," Pedersen said in a statement.

"The challenges ahead remain immense and we hear those who are anxious and apprehensive," Pedersen added. "Yet this is a moment to embrace the possibility of renewal. The resilience of the Syrian people offers a path toward a united and peaceful Syria."

Pedersen called for "stable and inclusive transitional arrangements" to smooth the transfer of power on the path to "a unified Syria, with its sovereignty, independence and territorial integrity, in a way that can receive the support and engagement of the entire international community."

Syrian refugee communities abroad are celebrating the fall of President Bashar al-Assad's government after a week-long lightning rebel offensive.

The civil war that erupted in 2011 has forced around 12 million Syrians -- more than half of the country's 2011 population of around 22 million -- from their homes. Around 5.4 million of these were still living abroad as of late 2022, per United Nations data.

Crowds gathered in cities in Turkey and Lebanon on Saturday night into Sunday morning to celebrate the news of Damascus falling to rebel forces advancing from the north and south.

Photos showed large crowds gathered in central Istanbul waving Syrian opposition and Turkish flags to celebrate the rebel victory.

Turkey and Lebanon host the largest number of Syrian refugees. Germany, Jordan, Iraq, Egypt and Sweden are also major centers for displaced Syrians.