The White House said Saturday it was "concerned" about apparent Russian attempts to "increase tension," as Ukraine said Russian forces had moved on regions outside of Crimea for the first time.
"We remain concerned about any attempt by Russia to increase tensions or threaten the Ukrainian people, and as we have long said, if Russia continues to take escalatory steps there will be consequences," National Security Council spokesperson Caitlin Hayden said in a statement provided to Business Insider.
The White House's latest warning to Russia came after Ukraine's Ministry of Foreign Affairs accused Russia of an "invasion" of its mainland — and the day before a controversial referendum is set to determine if Crimea splits from Ukraine.
In a statement, Ukraine's foreign ministry said 80 Russian troops supported by four helicopter gunships and three armed combat vehicles seized a gas-pumping station near the village of Strilkove. The village sits in the region just north of Crimea, and appeared to be the first move by Russian forces outside Crimea. Russian forces have occupied Crimea for much of the last month.
The foreign ministry further declared in its statement that it "reserves the right to use all necessary measures to stop the military invasion by Russia," and demanded that Russia "immediately withdraw its military forces from the territory of Ukraine."
An unnamed Russian official told The Telegraph the move had been made to guard against "terrorist attacks." Russia's foreign ministry said, meanwhile, it had received "many requests" to protect people in Ukraine.
Tensions have increased in regions outside of Crimea recently. At least one person died and 17 were wounded in clashes in the city of Donetsk on Thursday. Many observers, including U.S. Sen. Marco Rubio (R-Fla.) on Saturday, have accused Russian provocateurs of attacking Ukrainians.
Crimea is set to hold a referendum on Sunday that will determine whether the region secedes from Ukraine. It is largely expected Crimea will vote to secede from Ukraine and possibly vote in favor of annexation with Russia.
In New York on Saturday, Russia vetoed a U.S.-led resolution at the United Nations Security Council that would have declared the referendum illegal. The U.S. and other Western countries view the referendum as illegitimate and illegal, and have threatened Russia and President Vladimir Putin with sanctions.
U.S. Secretary of State John Kerry met for approximately six hours on Friday with Russian Foreign Minister Sergei Lavrov, but there was no progress toward a "common vision" on Ukraine.
Kerry said Lavrov made it clear Putin would not make any further decisions on Ukraine until after the referendum on Sunday. Kerry reiterated, however, that the United States and the international community would not recognize the expected results of the referendum.
"That is a decision of enormous consequence with respect to the global community," he said.
Lavrov said after the meeting with Kerry that Russia "doesn't and can't have any plans to invade southeastern regions of Ukraine."