The United States reiterated its condemnation of Russia's annexation of Crimea, vowing to maintain related sanctions until Moscow returns the strategic Black Sea peninsula to Ukraine.
"Crimea is a part of Ukraine. The United States again condemns the Russian occupation of Crimea and calls for its immediate end," said acting US State Department spokesman Mark Toner in a statement marking the three-year anniversary of Moscow's takeover of Crimea.
"Our Crimea-related sanctions will remain in place until Russia returns control of the peninsula to Ukraine."
Russia annexed the Ukrainian peninsula following a military intervention and a hastily organized referendum, which was rejected by the international community.
"The United States does not recognize Russia's 'referendum' of March 16, 2014, nor its attempted annexation of Crimea and continued violation of international law," said Toner.
"We once again reaffirm our commitment to Ukraine's sovereignty and territorial integrity."
In the statement the US also called on Russia to "cease its attempts to suppress freedom of expression, peaceful assembly, association, and religion" among Crimean Tatars, ethnic Ukrainians, pro-Ukrainian activists and journalists.
Russia's move to annex Crimea shattered ties between the two ex-Soviet neighbors and sent relations between Moscow and the West plummeting to their lowest point since the Cold War.
The US and the European Union reacted to the annexation of Crimea by imposing economic sanctions on Russia and Putin's inner circle.