US military carries out Open Skies flight over Ukraine

The U.S. said Thursday it and unspecified allies have conducted an "extraordinary flight" over Ukraine amid heightened tensions between Russia and Ukraine.

"The timing of this flight is intended to reaffirm U.S. commitment to Ukraine and other partner nations," the Pentagon said in a statement.

The flight comes under the auspices of the Open Skies Treaty, which allows for unarmed aerial observation flights in signatory countries.

The announcement follows Russia's seizure of two Ukrainian naval ships and a navy tugboat along with 24 crew off the Crimea Peninsula in late November. Moscow accuses the vessels of entering its waters and provoking a conflict.

In announcing Thursday's flight, the Pentagon pointed to the Russian attack, which it called "unprovoked," and a "dangerous escalation in a pattern of increasingly provocative and threatening activity.

"The United States seeks a better relationship with Russia, but this cannot happen while its unlawful and destabilizing actions continue in Ukraine and elsewhere," it said.

On Wednesday, CNN reported the U.S. is preparing to sail a naval warship into the Black Sea. The news network cited three anonymous officials who said the Pentagon has requested the State Department inform Turkey of the possible action.

The U.S. is required to notify the country under the terms of the 1936 Montreux Convention, which governs the movement of military ships through the strategic Istanbul and Çanakkale waterways which connect the Mediterranean to the Black Sea.

The officials said the planned naval movement was in response to Russia's seizure of the Ukrainian ships and personnel.

Russia and Ukraine have been at loggerheads since 2014, when Russia annexed Crimea from Ukraine following a controversial referendum.

The international community views the annexation as illegal and the election Russia uses to justify it as illegitimate.