The White House said Wednesday that Russia was "directly responsible" for casualties in Crimea amid reports that a Ukrainian soldier had been killed and the head of the navy had been detained by pro-Moscow forces.
"We strongly condemn Russia's use of force in Crimea," White House press secretary Jay Carney said. "The Russian military is directly responsible for any casualties that its forces, whether they be regular uniformed troops or irregulars without insignias, inflict on Ukrainian military members in Crimea."
"The continued efforts by Russian forces to seize Ukrainian military installations are creating a dangerous situation," Carney said.
Ukrainian acting president Oleksandr Turchynov warned Wednesday that if pro-Russian forces did not release Ukrainian "hostages" in Crimea, the government would respond with "an adequate response," according to a statement obtained by Agence France-Presse.
Interim Ukrainian Prime Minister Arseniy Yatsenyuk denounced the killing of a Ukrainian soldier as a "war crime" on Tuesday.
The White House said it was "working on" additional responses to Russia's takeover of the Crimea region, although Carney sidestepped questions about what specifically those "costs" would look like or when they would be announced.
"We will continue to make clear that this kind of behavior, you know, will result in costs to Russia and isolation to Russia," Carney said. "And Russia will need to assess the impact of those costs and understand that they will grow more severe and compound over time."
Carney did say that a military response was "certainly not at the forefront of discussions," with the U.S. instead looking to de-escalate the crisis.
The press secretary also dodged questions about whether the U.S. would tap its strategic oil reserve or increase natural gas exports to try and put pressure on Russia's economy. He warned that any attempts by the Kremlin to interfere with the flow of energy to Europe would end up damaging the Russian economy.
But Carney also conceded that diplomatic relations with Moscow had deteriorated, saying the "intensity of the disagreements" had increased with the crises in Syria and Ukraine.
"I don't think there's any doubt that relations between Russia and the West are not in a good place right now," Carney said.