(CNN) A US Air Force OC-135 observation aircraft conducted an "extraordinary flight" Thursday under the Open Skies treaty "to reaffirm US commitment to Ukraine" amid Russia-Ukraine tensions, the Pentagon said.

Although the Open Skies Treaty gives each of the 34 state parties the right to gather information about the military forces and activities of other state parties, an extraordinary flight allows for countries to conduct the flights on a bilateral basis, in this case with the agreement of just Ukraine and the US.

Russia, a signatory to the treaty, would have to approve a normal flight as part of a larger package that also includes the proposed flights of all 34 parties to the treaty.

"The timing of this flight is intended to reaffirm US commitment to Ukraine and other partner nations," Pentagon spokesman Eric Pahon told CNN.

"Russia's unprovoked attack on Ukrainian naval vessels in the Black Sea near the Kerch Strait is a dangerous escalation in a pattern of increasingly provocative and threatening activity," he added.

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