U.S. President Barack Obama says Russia must pull back its troops from the Ukrainian border and begin negotiating to defuse tensions.
In an interview with CBS News, Obama said Russia's military moves may be no more than an effort to intimidate Ukraine. But he added that Russia may have "additional plans.
"On Thursday, the head of Ukraine's national security council, Andriy Parubiy, said Russia has close to 100,000 troops along Ukraine's borders in the north, south, and east. He said Russian forces are in full readiness to strike.
Russia says the soldiers are involved in "springtime exercises" and has assured the United States they will not cross the border.
Western experts believe the number of Russian forces near eastern and southern Ukraine is close to 30,000.
Russia: UN resolution 'counterproductive'
Also Friday, Russia described as "counterproductive" a U.N. resolution that refuses to recognize its annexation of the Crimean peninsula from Ukraine. Russia's Foreign Ministry said the U.N. General Assembly resolution will only complicate efforts to settle Ukraine's internal political crisis.
The ministry accused Ukraine of seeking to distract from domestic tensions by blaming its problems on Russia.
The U.N. General Assembly passed the non-binding resolution on Thursday, with 100 countries in favor, 11 opposed and 58 abstaining.
Crimea's majority Russian residents voted to break away from Ukraine and join Russia in a referendum earlier this month that Western powers deemed illegal.
Ousted Ukrainian president Viktor Yanukovych called Friday for referendums to determine the status of all Ukrainian regions. He said only a nationwide referendum and not an early presidential election can stabilize Ukraine and preserve its sovereignty and integrity.
Meanwhile, Reuters reports that Russia's defense minister told President Vladimir Putin on Friday that all Ukrainian servicemen loyal to Kyiv had left Crimea and the Russian flag was flying over all military sites on the Black Sea peninsula.
Warships, war planes and other military hardware seized by Moscow will be returned to the Ukrainian army, Defense Minister Sergei Shoigu told Putin at a a meeting with senior Russian military officers.
Also Friday, Russia's Foreign Ministry said in a statement that restrictions imposed by Switzerland on military exports to Russia over events in Ukraine were counterproductive and not in line with the country's policy of neutrality.
Some information for this report provided by Reuters.