President Joe Biden on Sunday said that former Syrian dictator Bashar Assad's fall from power is a "fundamental act of justice."

“We will remain vigilant,” Biden said during his remarks, according to The Associated Press. “Make no mistake, some of the rebel groups that took down Assad have their own grim record of terrorism and human rights abuses.”

Early Sunday morning, Islamist rebels stormed the Syrian capital of Damascus, resulting in Assad fleeing the country. 

Assad’s reported departure was a pivotal moment in Syria’s 13-year civil war, potentially altering the balance of power across the Middle East where Iran and Russia have backed Assad for years.

"Rebel forces have forced Assad to resign his office and flee the country," Biden said during his speech. "We're not sure where he is but there's word that he's in Moscow. At long last, the Assad regime has fallen."

He added that the regime killed thousands of innocent Syrians. 

“President Assad of Syria has arrived in Moscow," Russian media reported, according to The Times of Israel. "Russia has granted them (him and his family) asylum on humanitarian grounds.”