WASHINGTON, March 21- President Joe Biden confirmed Russia's use of hypersonic missiles in Ukraine, warning Russian President Vladimir Putin's "back is against the wall," which means he could resort to using more severe tactics as the war stretches into another week, USA Today reported.

Speaking at the Business Roundtable’s CEO Quarterly Meeting on Monday, Biden said Russia used the fast-flying missiles "because it's the only thing that they can get through" Ukrainian defenses. He called it a "consequential weapon" that's "almost impossible to stop."

"There's a reason they're using it," Biden said.

Russia has said it twice used its Kinzhal aviation missile system to strike targets in Ukraine. Hypersonic missiles can move at five times the speed of sound or more. The Russian military said these missiles are capable of hitting targets at a range of more than 1,200 miles, or roughly the distance from New York City to Kansas City.

Biden also said Putin didn't anticipate how unified NATO and western allies would be in a global response to his invasion of Ukraine. "The more his back is against the wall, the greater severity of the tactics he may employ," Biden warned.

Biden said false-flag maneuvers like accusing the U.S. of housing biological and chemical weapons inside Ukraine -- a claim the White House has vehemently denied -- could be a pretext to escalate attacks. (om/ez)