Russia has denied U.S. reports of a “threatening” buildup of its armed forces along the Ukrainian border, but did it in a way that may heighten suspicions about its plans.

 Pentagon officials rang alarm bells over continuing massing of Russian troops close to Ukraine that did not look like mere training.

“We've seen no specific indications that these -- that exercises -- are taking place,” Pentagon spokesman Rear Admiral John Kirby told reporters on Thursday.

U.S. military officials were quoted as suggesting that the numbers of Russian troops far exceed the amount needed for a training exercise, that there was no real evidence of exercises taking place and that the troops were concealing their positions.

The Russian Foreign Ministry said that several international and Ukrainian monitoring missions undertaken in mid-March «failed to detect any ‘aggressive preparations’ and any military activity other than those that were declared earlier» near the Russian border with Ukraine.

In a statement issued on Friday the Russian Foreign Ministry wondered why the U.S. and NATO ignored the “objective information” gathered by the inspection groups.

However, the Russian statement failed to address Western reports that the number of Russian troops near the Ukrainian borders had swelled in the past few days, that is, after March 20, when the international inspectors had already left Russia.   

U.S. defence officials told CNN on Friday that an estimated 40,000 Russian troops were deployed near the Ukrainian border, even though they said the exact number was difficult to assess on the basis of satellite imagery.

U.S. President Barack Obama on Friday urged Russia to stop “intimidating” Ukraine and to pull its troops back to “de-escalate the situation.”

“You've seen a range of troops massing along that border under the guise of military exercises,” he told CBS in an interview in Vatican City. “But these are not what Russia would normally be doing.”

He said the troop buildup may “be an effort to intimidate Ukraine, or it may be that they've got additional plans.”

Russia’s President Vladimir Putin on Friday thanked the military for preventing violence in Crimea and providing safe conditions for the region’s vote to split away from Ukraine.

 “The precise and professional performance” of the Russian servicemen “allowed avoiding provocations, preventing bloodshed and ensuring conditions for a peaceful and free referendum,” Mr. Putin said at a Kremlin ceremony of awarding higher ranks to top military commanders.

Meanwhile, Ukraine’s ousted President Viktor Yanukovych called for referendums in Ukraine to decide every region’s status within the country.

“I call on each reasonable citizen of Ukraine: don’t let the imposters use you! Demand a referendum on the determination of the status of each region within Ukraine,” Mr. Yanukovych said in a statement issued in Russia, where he fled after the “Maidan revolution” in Ukraine last month.

Ukrainian officials denounced the appeal as an attempt to fan separatism in Russian-speaking eastern and southern regions of Ukraine.

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