WASHINGTON - US Secretary of State John Kerry on Sunday condemned Russia's "incredible act of aggression" in Ukraine and threatened "very serious repercussions" from the United States and other countries including sanctions to isolate Russia economically.

"You just don't in the 21st century behave in 19th century fashion by invading another country on completely trumped up pre-text," Kerry told the CBS program "Face the Nation."

Kerry, however, added that Russia still has "a right set of choices" that can be made to defuse the crisis.

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