US Warns Russia of Isolation over Ukraine

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

"You just do not, in the 21st century, behave in 19th century fashion by invading another country on completely trumped up pre-text," Kerry told on American broadcaster CBS.

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

He also said that Moscow risked losing its place among the prestigious Group of 8 developed nations over its deployment of troops in Crimea.

Kerry warned Russian President Vladimir Putin, saying: "He is not going to have a Sochi G8; he may not even remain in the G8 if this continues. He may find himself with asset freezes on Russian business, American business may pull back, there may be a further tumble of the ruble."

The statement comes hours after the US, Canada, France and the United Kingdom have pulled out of the talks in preparation for a G8 meeting in Sochi scheduled for the summer of 2014, Al Jazeera reported.

The West is facing its biggest confrontation with Moscow since the Cold War after Putin declared the right to use force in Ukraine.