The UN Security Council is expected to vote on a resolution upholding Ukraine's territorial integrity.
The U.S.-sponsored draft also declares that a March 16 referendum on whether the Ukrainian region of Crimea should break away and possibly join Russia "can have no validity."
Supporters are aware Russia is virtually certain to veto the resolution.
But U.S. Ambassador Samantha Power said the measure is aimed at "showing the extent of Russia's isolation as it pursues a nonpeaceful path."
Supporters are certain that 13 of the 15 council members will vote "yes" and are hoping that China, a close ally of Russia, will abstain.
In Russia, opponents of Moscow's actions in Crimea and the planned referendum are expected to hold an unsanctioned rally in the capital on Saturday.
A six-hour meeting in London March 14 between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov failed to delay the referendum.
Lavrov said Moscow will make no decisions about Crimea's future, including whether to embrace it as a new territory, until after the March 16 vote.
"We have already said through President [Vladimir] Putin's statement, that we will respect the choice of the Crimean people, or Crimean peoples, because there are several [peoples] there," he said. "And we will state our attitude towards the results of the referendum when the results are known. The Crimean parliament has adopted the declaration which stated the independence already and expressed the hope that the Crimeans will confirm that at the referendum."
Kerry said the referendum amounted to a "backdoor annexation" of the Ukrainian region.
"Neither we nor the international community will recognize the results of this referendum," he said. "We also remain deeply concerned about the large deployments of Russian forces in Crimea and along the eastern border with Russia."
Late on March 14, fatal clashes between bands of pro-Russian and pro-Ukrainian demonstrators were reported in Kharkiv.
Ukrainian Interior Minister Arsen Avakhov confirmed that two people were killed and several wounded in a shootout in the eastern city of Kharkiv.
Avakhov wrote on his Facebook page on March 15 that some 30 people "from both sides" had been arrested overnight.
The identities of those killed were not given.
Avakhov added that a policeman had been "severely" injured and that weapons were seized. He said an investigation is under way.
The violence comes one day after clashes in the eastern city of Donetsk left one pro-Ukraine protester dead and several others injured.
With reporting by AP, Interfax, and Reuters