The U.S. is moving toward sailing a Navy warship into the Black Sea in defiance of what it considers a sharp rise in tensions between Ukraine and Russia.

The Pentagon has asked the State Department to begin the process of requesting permission from Turkey to sail vessels into the Black Sea, which borders both Ukraine and Russia and serves as the sole maritime access to the Sea of Azov, a flashpoint for a series of confrontations between Moscow and Kiev in recent weeks.

The maneuver, known in military parlance as a "freedom of navigation" exercise, would risk drastically escalating the possibility of conflict between the Russia, the U.S. and Ukraine, which Washington has supported militarily since Russia annexed Crimea in 2014 and began supporting separatist forces in the country's east.

CNN first reported the Pentagon's request. It's unclear, however, whether the U.S. Navy plans to follow through on entering the Black Sea.

Access to the sea through the Bosporus Straits is governed by the 1936 Montreux Convention Regarding the Regime of the Straits, requiring governments to secure permission from Turkey 15 days before passage.

"The U.S. files Montreux Convention requests regularly but doesn't always follow through by sending a ship," Pentagon spokesman Eric Pahon says.

Russia has filed more than three dozen requests in recent months but only actually sailed a ship through the Bosporus roughly half the time, a defense official says, speaking on the condition of anonymity.

Both Russia and Ukraine in recent months have increasingly militarized the Azov Sea , which borders the Crimean Peninsula. Governed by a sharing agreement between Moscow and Kiev, it provides Ukraine with the only maritime access to critical port cities like Mariupol and Berdyansk and is home to a key Russian naval group based on Crimea. In recent days, Moscow deployed ships to block the Kerch Strait – the sea's only access point. Russian security services opened fire on Ukrainian vessels in late November as they attempted to traverse the straits and detained 24 Ukrainian sailors.

Wednesday's news came hours after CNN also revealed that a U.S. warship had sailed through the Sea of Japan in defiance of Russian claims in the region. It's unclear whether the two operations would be part of a single strategy, as ships operating in those regions fall under different Navy headquarters.

A spokesman at the Navy's 6th Fleet, which oversees operations in Europe and Africa, said it is "always prepared to respond when called."

"We routinely conduct operations to advance security and stability throughout the U.S. 6th Fleet area of operations to include the international waters and airspace of the Black Sea. We reserve the right to operate freely in accordance with international laws and norms," the spokesman said.

Secretary of State Mike Pompeo hinted Tuesday at further action to deter Russia in retribution for its recent activities. Speaking in Brussels after issuing an ultimatum to Moscow regarding its nuclear program, Pompeo said the recent Russian actions were "lawless and unacceptable and deterrents must be restored."

"We hope that the Russians will return the sailors that they're holding today, just immediately. And we will collectively develop a set of responses that demonstrate to Russia that this behavior is simply unacceptable," Pompeo said.

Russian officials have anticipated a U.S. response to the ongoing dispute. The chairman of the defense committee for the Russian State Duma said Wednesday he expects "dirty tricks" from the U.S. in response to the ongoing disputes around the Kerch Strait and threatened legal action if the Trump administration follows through.

"They have a wide spectrum of options here," Vladimir Shamanov, of the Russian legislature's lower house, said according to state news service Tass . Shamanov said the U.S. could potentially block Russian ships from accessing ports or maneuvering freely, as he claimed American ships did to Russian vessels supporting operations in Syria.