UNITED NATIONS — Russia on Saturday vetoed a U.N. resolution that declared Sunday’s referendum on the future of Ukraine’s Crimean Peninsula illegal, but its 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. The 13 other council members voted “yes.”

The resolution would have reaffirmed the council’s commitment to Ukraine’s “sovereignty, independence, unity and territorial integrity.”

Supporters of Ukraine’s territorial integrity had hoped to demonstrate the strength of opposition to Russia’s takeover and possible annexation of the Crimean Peninsula in the vote.

The resolution would also have declared that Sunday’s 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.”

The draft resolution also urged all parties “to pursue immediately the peaceful resolution of this dispute through direct political dialogue,” to protect the rights of minorities in Ukraine.

China is sensitive to the issue of territorial integrity because of Tibet and other restive areas, and China’s U.N. Ambassador Liu Jieyi reiterated Beijing’s support again Thursday for Ukraine’s sovereignty and territorial integrity, and for not interfering in other countries’ internal affairs.

The Security Council has held six meetings on Ukraine in less than two weeks but has been unable to take any action because of Russia’s veto power.