WASHINGTON: The US 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 US 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.