Russia has vetoed a United Nations Security Council resolution urging countries not to recognize the results of this Sunday's referendum on whether Crimea breaks away from Ukraine to join Russia.
Russia was the only member to vote against the measure Saturday. Thirteen other members voted for it while China abstained, saying the resolution would lead to confrontation and complications.
The resolution would have affirmed Ukrainian sovereignty by declaring that the referendum has "no validity."
China's abstention could mean more isolation of Moscow for its support of the Crimean referendum.
U.S. Ambassador Samantha Power called the resolution's defeat "a sad and remarkable moment."
Russian Ambassador Vitaly Churkin said the resolution ran counter to the principles of international law.
Crimea is a primarily ethnic-Russian majority region of Ukraine. Moscow says it has the right to protect its interests in Crimea.
Meanwhile, Ukraine's Foreign Ministry says Russian forces have seized the village of Strilkove, near the Crimean border.
There are no reports of shots being fired, but the Ministry calls the takeover an "invasion" and demands the Russian soldiers leave.
But Ukrainian border guards say the Russians are only guarding a gas pumping station in the town.
Elsewhere, supporters and opponents of Russian action in Crimea rallied Saturday.
A large pro-Russian demonstration turned violent in the eastern city of Donetsk. Some protesters pushed their way past police and kicked in the glass windows and doors of the Ukrainian Security Service Building. The protesters stormed the building where they caused further damage.
Hundreds marched in Kyiv demanding Crimea remain part of Ukraine, while in Moscow, thousands of supporters of the referendum waved Russian and Soviet flags as they marched to Moscow's Revolution Square.
Opponents held a separate rally waving Ukrainian flags. Some said they fear Russian intervention in Crimea could lead to war.
Samantha Power, US Ambassador to UN:
"The truth is that this resolution should not have been controversial. It was grounded in principals that provide the foundation for international stability and law - Article 2 of the U.N. Charter - the prohibition on the use of force to acquire territory and respect for sovereignty, independence, unity and territorial integrity of member states. These are principals that Russia agrees with and defends vigorously all around the world -- except, it seems, in circumstances that involve Russia."
Vitaly Churkin, Russian Ambassador (English interpreter):
"We cannot go along with its basic assumption, that is declaring illegal the 16 March planned referendum where the very people of the Crimean republic will determine their future."
Liu Jieyi, Chinese Ambassador (English interpreter):
"The drafting of the draft resolution by the Security Council, at this juncture, will only result in confrontation and further complicate the situation."