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Caption:Russia's President Vladimir Putin looks on while speaking with journalists in Itamaraty Palace in Brazilia, early on July 17, 2014. The United States and Europe strengthened sanctions on Moscow over Ukraine yesterday, with President Barack Obama taking his first direct swipes in the finance, military and energy sectors of the Russian economy. Putin warned the biting sanctions will boomerang and hit back at US national interests, will inflicting 'very serious damage' on an already tattered US-Russia relationship. AFP PHOTO / RIA-NOVOSTI / POOL / ALEXEI NIKOLSKY (Photo credit should read ALEXEI NIKOLSKY/AFP/Getty Images)
Caption:Russia's President Vladimir Putin looks on while speaking with journalists in Itamaraty Palace in Brazilia, early on July 17, 2014. The United States and Europe strengthened sanctions on Moscow over Ukraine yesterday, with President Barack Obama taking his first direct swipes in the finance, military and energy sectors of the Russian economy. Putin warned the biting sanctions will boomerang and hit back at US national interests, will inflicting 'very serious damage' on an already tattered US-Russia relationship. AFP PHOTO / RIA-NOVOSTI / POOL / ALEXEI NIKOLSKY (Photo credit should read ALEXEI NIKOLSKY/AFP/Getty Images)

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Russia denies invasion of Ukraine

Meanwhile, a UK source tells CNN there are up to 5,000 Russian troops in Ukraine. CNN's Diana Magnay reports.

Russia denies invasion of Ukraine

Meanwhile, a UK source tells CNN there are up to 5,000 Russian troops in Ukraine. CNN's Diana Magnay reports.