Lithuania has handed over an alleged Belarusian spy to Polish authorities.
Warsaw accuses Sergei Monic of sending information vital to Polish national security to foreign intelligence services.
Lithuanian media say the information includes lists of employees at the Polish foreign ministry and other documents.
Monic was arrested in Vilnius in November on a Polish warrant. He has denied the charges and claims he was set up by a Polish acquaintance. He also says a treaty between Belarus and Lithuania should have prevented his extradition.
Ties between Poland and Belarus have been sour in recent years. Belarus has a large ethnic Polish population. Minsk has accused Polish institutions of fomenting rebellion, leading to a number of tit-for-tat diplomatic expulsions.
Some information for this report was provided by AFP.