Ukrainian military officer Nadezhda Savchenko speaks to journalists shortly after her capture in Luhansk, Ukraine, on June 19, 2014. She was apparently captured by pro-Russian insurgents during fighting in eastern Ukraine. But she is being held in Russia, which claims she was arrested in that country. Ukrainian officials say the separatists handed her over to Russia. Igor Golovniov/AP hide caption

itoggle caption Igor Golovniov/AP

In this June 27, 2006, file photo U.S. military guards walk within Camp Delta at the Guantanamo Bay U.S. Naval Base, Cuba. The U.S. announced the transfer of four detainees from Guantanamo to Oman; one will go to Estonia. Brennan Linsley/AP hide caption

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Estonian President Toomas Hendrik Ilves (left), with intelligence officer Eston Kohver in 2010. Kohver was arrested by Russian police on spying charges, but Estonian officials called it an illegal kidnapping. AP hide caption

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A column of Russian troops prepares to leave the checkpoint at a bridge over the Inguri River in Western Georgia, in October 2008, after securing the secession of Georgia's breakaway South Ossetia region. Levan Gabechava/Reuters/Landov hide caption

itoggle caption Levan Gabechava/Reuters/Landov

Residents of the Estonian capital of Tallinn can use public transportation for free after purchasing a special card for 2 euros. Raigo Pajula/AFP/Getty Images hide caption

itoggle caption Raigo Pajula/AFP/Getty Images