"The Vilnius county court has received the appeal, which was forwarded to the Lithuanian Court of Appeals," Vilma Budėnienė, spokeswoman for the Court of Appeals, told BNS on Thursday.

Lithuanian prosecutors say the 40-year-old man who was detained in 2015 was an officer of the Kaliningrad branch of the Russian Federal Security Service (FSB).

The Vilnius court ruled in early July had used forged documents in an effort to conceal his identity and unlawfully cross the state border on multiple occasions, sentencing him to ten years in prison.

The law-enforcement earlier said he had aimed to recruit officers of the VIP Protection Department to plant bugs in the office and residence of Lithuanian President Dalia Grybauskaitė.

The Lithuanian State Security Department said this was the first case in the country when a staff officer of a Russian security service had been detained.

His lawyer Galina Kardanovskaja said that her client denied his guilt.