The United States and Russia have failed to reach a diplomatic breakthrough over the future of Ukraine. as the tensions once again turned deadly on Saturday.
During talks in London, the U.S. Secretary of State John Kerry could not persuade the Russians to postpone Sunday's vote in Crimea on joining Russia.
Now Europe and the U.S. are planning to impose fresh sanctions on Moscow by Monday.
Violent clashes between rival protest groups in eastern Ukraine have lead to the deaths of at least three people.
Russian foreign ministry says the violence shows Ukraine's authorities had lost control.
Meanwwhile, international observers invited by Russia and Crimean authorities have arrived in Simferopol , the administrative center of Crimea, ahead of Sunday's referendum.