U.S. closely monitoring Syria's chemical weapons after Assad ouster

The United States is closely monitoring Syria's chemical weapons stockpile following the rapid fall of the Assad regime and views the issue as a "top-tier" priority in the region, according to a senior Biden administration official.

The U.S. is focused on ensuring that Syria's chemical weapons don't fall into the wrong hands after the collapse over the weekend of Syrian President Bashar al Assad's decades-long rule, the official said.

"We are doing everything we can to prudently ensure that those materials are either not available to anyone or are cared for," the official said Sunday, speaking on background to brief reporters on the latest developments in Syria.

National security experts are "fairly confident" that Syria's chemical weapons stockpile can be "destroyed" or secured, the official added.

The senior administration official did not provide further details, but said the Biden administration isn't planning to send U.S. troops into Syria to secure or destroy chemical weapons held by the former Assad regime.

The extent of the regime's chemical weapons stockpile is unclear. Assad's government used chemical weapons multiple times against rebel groups and Syrian civilians during the nation's ongoing 13-year civil war.

U.S. intelligence agencies have reportedly closely monitored Syria's chemical weapons storage facilities in recent days as rebel groups made a lightning-fast push to topple the Assad regime.

Opposition groups moved into the capital Damascus overnight on Saturday in a stunning turn of events after a yearslong stalemate in the war. The development threatened to further destabilize a region already mired in fighting between Israel and the Iranian-backed groups Hamas and Hezbollah.

Assad fled Syria on Saturday, arrived in Moscow on Sunday and was granted political asylum by the Russian government, according to Russian news agency Tass.

Russia and Iran had helped prop up Assad throughout the conflict, serving as powerful proxy forces in a war with an estimated death toll of more than 500,000 people. Millions more have been displaced since the war started in 2011.

President Joe Biden on Sunday addressed the situation in Syria, saying the U.S. government would seek to ensure Syria's stability after Assad's ouster. He also issued a warning to rebel groups who fought to take control of the country.

"Make no mistake, some of the rebel groups that took down Assad have their own grim record of terrorism and human rights abuses," Biden said in remarks from the White House.

Biden said the U.S. would not let ISIS or other terrorist groups gain a new foothold in the country with Assad out of power.