"We strongly support Ukraine's territorial integrity and sovereignty," spokesman Jay Carney told reporters at a regular press briefing, adding "We expect other nations to do the same."

　　Security forces in Crimea, an autonomous republic in southern Ukraine, have been put on alert after armed groups seized local government and parliament buildings Thursday, interim Interior Minister Arsen Avakov said.

　　Ukraine's acting President Alexandr Turchynov also warned that any troop movements at Russia's Black Sea fleet based in Crimea " will be considered as military aggression."

　　Carney said Washington was "closely watching" Russia's military exercises along the Ukrainian border. "We expect Russia to be transparent about these activities and to avoid provocative actions," he added. "We urge them not to take any steps that could be misinterpreted or lead to a miscalculation during a very delicate time."

　　Russian Defense Minister Sergei Shoigu said the snap drills had been aimed to check the military's combat readiness and were not related to Ukraine.

　　U.S. Secretary of State John Kerry, who spoke to his Russian counterpart Sergey Lavrov over the phone Thursday, said he was assured of Russia's respect for the sovereignty of Ukraine. Kerry urged Russia to match its words with actions.

　　"We believe that everybody now needs to step back and avoid any kind of provocations," the top American envoy said.

　　Both Kerry and Carney welcomed Ukrainian parliament's decision Thursday to establish a new government.

　　Ukrainian president Viktor Yanukovych was ousted by the parliament on Feb. 22, one day after he signed a deal with opposition leaders in efforts to quell surging violence in the country.

　　Russia has called back its ambassador to Ukraine for " consultations" in response, while Russian Prime Minister Dmitry Medvedev on Monday questioned the legitimacy of Ukraine's new authorities, saying "masked and armed people are not the partners for a dialogue."