Russia vetoed a U.N. resolution declaring Sunday’s referendum on the future of Ukraine’s Crimean Peninsula illegal, and close ally China abstained in a show of Moscow’s isolation.

Supporters of the U.S.-sponsored resolution knew that Russia would use its veto. But they put the resolution to a vote Saturday morning to show the strength of opposition to Moscow’s takeover of Crimea in the U.N. Security Council.

The final vote was 13 members in favor, China’s abstention, and Russia as a permanent council member casting a veto.

The resolution would have reaffirmed the council’s commitment to Ukraine’s “sovereignty, independence, unity and territorial integrity.” It would have declared that the referendum on whether Crimea should become part of Russia “can have no validity, and cannot form the basis for any alteration of the status of Crimea.”