Estonian internal security officer Eston Kohver, sentenced by a Russian court to 15 years in prison for espionage last month, did not appeal his sentence, which therefore come into force Friday, Interfax reported.
Previously, Kohver's lawyer Yevgeny Aksyonov told Interfax that his client had not asked him to appeal the sentence.
FSB officers detained Kohver on Russia's border with Estonia in September last year. He was accused of crossing the border illegally while carrying firearms. Estonian authorities argued that Kohver was illegally detained on Estonian territory.
Brussels and Washington said Russia violated international law in their handling of the case and expressed concern that Kohver's rights to a proper legal defense were violated. In August, the Estonian government announced plans to build a fence along its eastern border with Russia.