Any Russian ultimatum to Ukraine would be 'dangerous': US

WASHINGTON (AFP) - Any Russian ultimatum to Ukraine threatening a possible attack would be a "dangerous escalation" of the tensions in Crimea, a US official said on Monday.

Washington was working to find out if Moscow has demanded Ukrainian leaders surrender or face an all-out assault. "If true" it would be "a dangerous escalation of the situation and we would hold Russia directly responsible," said State Department spokeswoman Jen Psaki.