A sign at the Russia-Estonian border
Estonian Internal Security Service agent Eston Kohver was abducted on Sept. 5 after Russian Federal Security Service agents crossed into Estonia to take him. Reuters

An Estonian intelligence officer who was abducted by Russian Federal Security Service (FSB) agents from within Estonia's borders will not be released from Lefortovo prison in Moscow until at least spring 2015. The ruling was passed down by a judge late Monday evening, and diplomatic tensions between the two countries increased after Estonian officials were barred from participating in the court hearing, according to a Baltic Times news report.

"The abduction of Eston Kohver from Estonian territory and his subsequent detention in Russia are violations of international law," said Estonian Foreign Ministry spokeswoman Mariann Sudakov to an Estonian public broadcaster.

Kohver was abducted at gunpoint around 8 kilometers from the Russian border in southeastern Estonia on Sept. 5. According to the Estonian Internal Security Service (KaPo), Kohver was fulfilling his official duties when unknown Russian FSB agents forced him to cross the border into Russia, where he was accused of espionage and locked up.

Kohver believed he was meeting an informant as part of an organized crime investigation but instead walked into a trap. The meeting took place at 9 a.m., local time, roughly 5 miles from the Estonia-Russia border. Kohver had armed security guards, but they were unable to get to him in time because Russian agents used flash bombs and jammed communications.

The Russian government has suggested that Kohver was spying inside Russia. A joint investigation by Russian and Estonian border guards in September discovered impact craters from the grenades and footprints near a sand cordon on the border.

Head of the Estonian KaPo Arnold Sinisalu said that agents were under strict instructions not to travel into Russia, while also saying that the security team accompanying Kohver was only able to react after he had been dragged through the woods into Russia.