US will ‘clean up’ after Daesh seizes Syria's Palmyra

It will now fall to the U.S. to retake a city of ancient treasures that Daesh recently retook from Syrian President Bashar al-Assad's forces, the White House said Thursday.

"It's now U.S. members of the military that are now going to have to go in and clean up the mess again that was created by Syria with the backing of the Russians," spokesman Josh Earnest told reporters.

He said the threat posed by Daesh has actually increased because when the group seized Palmyra, it took not only the city, but "all of the military equipment that the Assad regime, backed by Russia, had moved in there".

Deash retook the historically rich city last weekend from Syrian forces who had formerly ousted the terror group nine months ago. At the time, Damascus hailed the development with much fanfare, hosting a Russian symphony orchestra concert among the ruins.

When they first held the city, Daesh blew up the 2,000-year-old Temple of Bel and other irreplaceable archeological sites. Concerns have been renewed that the city, which hosts a UNESCO world heritage site, could face a new wave of demolitions with militants back in control.

Syrian and Russian forces had recently diverted much of their resources to retake the northern city of Aleppo, likely draining the effort to hold the city.

"I'm gravely concerned about the danger that is now heightened because of Russia's failed strategy," Earnest said.

Russia has been a principal backer of Assad, alongside Iran and Lebanese Hezbollah. It has waged a widespread air campaign in the country and deployed its special forces to fight what it calls "terrorists" in the country - shorthand used by Moscow and Damascus for all armed opposition groups.