President Barack Obama on Friday said Russia's troop buildup on the Ukraine border was out of the ordinary and called on Moscow to pull its military back and begin talks to defuse tensions.
"You've seen a range of troops massing along that border under the guise of military exercises," he told CBS "This Morning" in an interview in Vatican City. "But these are not what Russia would normally be doing."
Obama said the moves might be no more than an effort to intimidate Ukraine, but also could be a precursor to other actions.
"It may be that they've got additional plans," he said.
Meanwhile, Russia's defense minister told President Vladimir Putin on Friday that all Ukrainian servicemen loyal to Kiev 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 meeting with senior Russian military officers.
U.S. and European security agencies estimate Russia has deployed military and militia units totaling more than 30,000 people along its border with eastern Ukraine, according to U.S. and European sources familiar with official reporting.
The current estimates represent what officials on both sides of the Atlantic describe as a continuing influx of Russian forces along the Ukraine frontier, the sources said.
The 30,000 figure represents a significant increase from a figure of 20,000 Russian troops along the border that was widely reported in U.S. and European media last week.
But U.S. and European security sources noted that these estimates are imprecise. Some estimates put current troop levels as high as 35,000 while others still suggest a level of 25,000, the sources said.
However, the sources said that U.S. and European government experts believe that there has been, and continues to be, a steady and noticeable buildup in the total number of Russian forces along the Ukrainian border, though some military units have rotated in or out of the area.
U.S. and European security sources said that the Russian force deployed along the Ukraine border includes regular military including infantry and armored units and some air support.
Also deployed are militia or special forces units comprised of Russian fighters, wearing uniforms lacking insignia or other identifying markings, similar to the first Russian forces to move into Crimea during Russia's recent military takeover there.
U.S. officials said that what Russian President Vladimir Putin actually plans to do with his forces deployed on the Ukraine border is unknown. Some officials say intelligence information available to policymakers regarding what Putin is thinking, and what he is saying to his advisors and military commanders, is fragmentary to non-existent.
But the portents are potentially ominous. "No one's ruling out the possibility of additional Russian military aggression," one U.S. official said.
Report: Russia agrees to turn over some weapons to Ukraine
Meanwhile, Putin says Ukraine could regain some arms and equipment of military units in Crimea that did not switch their loyalty to Russia.
Russian forces took control of Ukrainian military installations in Crimea this month after Russia formally annexed the Black Sea peninsula. Some Ukrainian servicemen reportedly joined Russian forces, while others withdrew.
Russian Defense Minister Sergei Shoigu on Friday told Putin that the Ukrainian withdrawal from Crimea is complete, Russian news agencies reported.
Putin approved Shoigu's proposal to turn over arms and equipment of the units still loyal to Ukraine, the report said.
No specifics were given on quantities, types of hardware, or timing.
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