Lyashenko represented Russia internationally at both the junior and senior levels. His first experience with Russia's junior team was at the 1997 World Junior Championships, recording three points in six games as Russia defeated the Czech Republic for the bronze medal. At the 1998 World Junior championships, Lyashenko again represented Russia, as the team captured a silver medal. In seven games at the tournament, he recorded three assists. Lyashenko captained Russia's team at the 1999 World Junior Championships, which were held in Winnipeg. The Russian team captured the gold medal, defeating Canada in overtime. Lyashenko scored three goals and added two assists in seven games. With the gold medal, Lyashenko and teammate Mikhail Donika became the only two players to win a medal of each colour (gold, silver and bronze) at the World Junior Ice Hockey Championships.