Fake referendums and mobilization are signs of Russian weakness and failure, U.S. Ambassador to Ukraine Bridget Brink said, stressing that the U.S. would never recognize Russia's claims to supposedly annexed Ukrainian territory.

"Sham referenda and mobilization are signs of weakness, of Russian failure. The United States will never recognize Russia's claim to purportedly annexed Ukrainian territory, and we will continue to stand with Ukraine for as long as it takes," Brink said on Twitter on Wednesday.