Ukraine's prime minister is to travel to the US for top level talks.
Arseny Yatseniuk says he'll go this week to discuss the Crimea crisis.
There have been clashes in Sevastapol, at rival rallies of pro-Russians and those loyal to Ukraine.
The British Foreign Minister William Hague says Russia's occupation of the peninsula will prove to be a "big miscalculation" in the long-term.
Ukraine's opposition leader Vitali Klitschko is accusing Russia of over aggression:
