The Russian parliament has approved President Vladimir Putin's request to use the Russian military in Ukraine's Crimea region, further raising tensions between the neighbors.
Saturday's vote made official what Ukraine's newly-established interim government has described as an ongoing deployment of Russian troops in the Black Sea peninsula of Crimea.
Russia's upper house of parliament also recommended that President Putin recall Moscow's ambassador from the United States.
That move comes just one day after U.S. President Barack Obama expressed concern about reports of Russian troop movements in Crimea and warned of consequences if Russia intervenes in Ukraine.
Crimea, part of Ukraine since the Soviet Union collapsed in 1991, has become the focus of turmoil that began months ago when Ukraine's now-ousted President Viktor Yanukovych rejected a deal with the European Union in favor of closer ties with Russia.
As the tensions surrounding Crimea escalated Saturday, pro-Russian protesters clashed violently with supporters of the new Ukrainian government in Ukraine's eastern city of Kharkiv.
Earlier Saturday, the newly appointed pro-Russian prime minister of Crimea, Sergei Aksyonov, claimed control of the region's military and other security forces. He appealed to Mr. Putin for help in restoring "peace and calm."
Ukraine's newly appointed Prime Minister Arseny Yatsenyuk, meanwhile, demanded Saturday that Russia stop what he called its "provocations" in Crimea, and said the Ukrainian military in the majority Russian area is on high alert.
Russia has said its troop movements in Crimea, where it leases a naval base in Sevastopol, conform to agreements with Ukraine. But Ukraine's acting defense minister said 6,000 additional Russian troops have been deployed on Ukrainian soil.
Ukraine also has refused to recognize the Crimean prime minister, with acting Ukrainian President Oleksandr Turchynov issuing a statement declaring Aksyonov's appointment a violation of Ukraine's constitution.
Aksyonov was appointed by the Crimean parliament earlier this week as tensions soared over Crimea's resistance to the new authorities in Kyiv, who took power last week.
VOA correspondent Elizabeth Arrott says unidentified soldiers and military vehicles have appeared in the Crimean region, well beyond their local base. She said at least a dozen were stationed outside parliament in the Crimean capital of Simferopol on Saturday. She also said she saw gunmen in camouflage at the Simferopol airport Friday.
There also are reports of Russian troops surrounding the state-run television station in Simferopol.
The head of Russia's upper house of parliament said Saturday she could not rule out the possibility that a limited contingent of troops could be sent to Crimea to ensure the security of the Black Sea fleet in Sevastopol and Russian citizens living in the region.
Crimea, placed under Ukrainian control in 1943 by then-Soviet leader Nikita Khrushchev, has a tiny border with Russia on its far eastern point. Most of the people living in Crimea are ethnic Russians, but the region also is home to ethnic Muslim Tartars who generally show disdain toward Russia.
Ukrainian President Turchynov on Friday called Russian actions in Crimea "naked aggression." He likened the actions to events that led up to Russia's 2008 invasion of Abkhazia - a pro-Russian region of Georgia.
In another development Saturday, Russia's Energy Ministry threatened not to continue Ukraine's gas price discount because of Ukraine's unpaid balance. Gazprom said Saturday that Ukraine's outstanding gas debt for 2013 and this year is $1.55 billion.