Shirokov made his international debut with Russia at the 2003 U-18 Junior World Cup, earning a silver medal while contributing four points in five games. He continued to play with the national under-18 team, helping Russia to the best records at the 2003 Four Nations and 2004 Five Nations Tournaments. At the 2004 IIHF World U18 Championships, he helped Russia to another gold medal in Minsk, Belarus, defeating the United States 3–2 in the final. Shirokov contributed two goals in six games.