Secretary of State John KerryJohn Forbes KerryFor the sake of national security, Trump must honor the Iran deal Bernie Sanders’s 1960s worldview makes bad foreign policy DiCaprio: History will ‘vilify’ Trump for not fighting climate change MORE told his Russian counterpart on Sunday that the ongoing vote in Crimea to secede from the Ukraine is “illegal.”

Kerry told Russian Foreign Minister Sergei Lavrov that the United States will not recognize the results of Sunday’s vote, which is widely expected to show support for the Ukrainian region of Crimea seceding and joining Russia.

Instead, Kerry told Lavrov that Russia should “support efforts by Ukrainians to address power sharing, decentralization through constitutional reform process,” according to the State Department’s Twitter feed.

Sunday’s call marks the latest communication between the two top diplomats, as the U.S. and Russia continue to face off over the latter nation’s aggressive moves toward Ukraine.

Russian military forces have amassed along the Ukrainian border, and some troops have even advanced to claim a natural gas plant outside of Crimea, which Ukrainian officials called an “invasion.”

Kerry and Lavrov met for six hours Friday to discuss the ongoing standoff, but left having made no progress toward a resolution.

Voters are heading to the polls in the Russian-speaking region of Crimea to vote on possible secession, but the U.S. and other Western nations have already said they will refuse to recognize the legitimacy of the vote.

Russia had to veto a United Nations resolution condemning the resolution Saturday, after the U.S. and nearly every other voting member nation backed it. China abstained.

The European Union on Sunday condemned what it called the “unprovoked violation of Ukraine’s sovereignty and territorial integrity” and reiterated its position that the EU considers the referendum as “contrary to the Ukrainian Constitution and international law.”

“The referendum is illegal and illegitimate and its outcome will not be recognized,” according to a statement from European Council President Herman Van Rompuy and European Commission President José Manuel Barroso.

“Only working together through diplomatic processes, including direct discussions between the Governments of Ukraine and Russia, can we find a solution to the crisis,” the European leaders said. “The European Union has a special responsibility for peace, stability and prosperity on the European continent and will continue pursuing these objectives using all available channels.”

EU officials called on Russia to withdraw its armed forces and said ministers will evaluate the situation on Monday in Brussels.

-- This report was originally posted at 12:38 p.m. and last updated at 1:54 p.m.