The ex-Soviet nation's top security agency, which is still known as the KGB, said Thursday that the arrested individuals are Belarussian nationals who have already confessed to trying to obtain defense and security information about Belarus and Russia.
Lithuanian foreign ministry spokesman Mindaugas Lasas was quoted by the RIA Novosti agency as saying that the allegations were "not true."
Since 1994, Belarus has been ruled by authoritarian President Alexander Lukashenko. Over the years, his government has arrested and imprisoned dozens of opposition activists, government critics and journalists.
Belarus has often accused Lithuania, which is part of the European Union, of supporting Lukashenko's opponents.