Ukraine says it refuses to act with force against Russia's "provocation" in Crimea - a southern Ukrainian region with strong ties to Russia - calling on Russia to halt all military movement in the area.
Ukrainian Prime Minister Arsenly Yatsenyuk said Saturday his country will not be drawn into a military conflict with Russia.
Meanwhile, the newly appointed prime minister of Crimea, Sergei Aksenov, has claimed control of all the region's security forces and has asked Russia's president for help in restoring "peace and calm."
Aksenov said Saturday any commanders of the forces who do not want to comply with his orders should leave. Aksenov was not specific about what kind of assistance he wants from Russian President Vladimir Putin.
Aksenov 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 dozen were stationed outside parliament in Simferopol Saturday.
Russia says its troop movements in Crimea fall within agreements with Ukraine, where it leases a naval base in Sevastopol.
The head of Russia's upper house of parliament (Valentina Matviyenko) said Saturday she could not rule out the possibility that a limited contingent of troops could be sent to Crimea to assure the security of the Black Sea fleet and Russian citizens living in the region.
Ukrainian officials say Russia has violated its airspace, an apparent reference to military helicopters that flew over the largely pro-Russian Crimean region. The officials also expressed concern over Russian naval maneuvers in the Black Sea.
Ukraine's interim president, Oleksandr Turchynov, said Friday Russian actions are "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 has threatened not to continue Ukraine's gas price discount because of Ukraine's unpaid balance. Gazprom said Saturday Ukraine's outstanding gas debt for 2013 and this year is $1.55 billion.
Ukraine's acting interior minister, Arsen Avakov, says Russian forces have taken control of the two main airports in Crimea. He calls this a "military invasion." Flights were halted Saturday from the airport of the Crimean capital of Simferopol.
VOA's Arrott, who flew into the Simferopol airport Friday saw gunmen in camouflage and carrying automatic weapons at the airport. But she described the situation as calm.
There are also reports of Russian troops surrounding the state-run television station in Simferopol. A Ukrainian official also says 2,000 Russian soldiers have landed at a military base near the capital.
Meanwhile, the Associated Press quoted Ukraine's State Border Guard Service as saying a Ukrainian coast guard base was surrounded by about 30 Russian marines.
On Thursday, gunmen seized control of government buildings in Crimea. Those gunmen raised the Russian flag over the buildings.
The Crimean parliament voted Thursday to dismiss the regional government and hold a referendum to determine Crimea's status in Ukraine. The referendum is set for May 25, the same day Ukraine will hold a presidential election.
Crimea is a Black Sea peninsula in southern Ukraine, which has a tiny border with Russia on its far eastern point. The late Soviet leader Nikita Khruschchev placed it under Ukrainian control in 1954 and it became part of Ukraine when the Soviet Union collapsed in 1991.
Much of the Crimean population is pro-Russian and Russia's Black Sea naval fleet has a headquarters in the Crimean city of Sevastopol. Crimea is also home to ethnic Muslim Tartars who generally show disdain towards Russia.
The Ukrainian parliament approved a new interim government Thursday led by new prime minister Arseniy Yatsenyuk.
Mr. Yatsenyuk has accused the government of ousted president Viktor Yanukovych of stealing $70 billion from the treasury and sending the money to offshore accounts. He also says $37 billion of credit it received has disappeared, leaving Ukraine with severe financial problems.
Judicial authorities in Geneva have opened an investigation into alleged money laundering by Mr. Yanukovych and his son. The Swiss government also announced it is freezing the assets of 20 Ukrainian officials.