Prime Minister Yoshihiko Noda on Wednesday welcomed Barack Obama's re-election as U.S. president, expressing hope to deepen the bilateral alliance amid Japan's territorial tensions with China.

"I've issued a message to congratulate President Obama on his re-election. I'll continue to cooperate with him," Noda told reporters at his office after Obama was assured of victory in Tuesday's election.

Chief Cabinet Secretary Osamu Fujimura told reporters: "The security environment in East Asia is severe, so the importance of the Japan-U.S. alliance has increased. We hope to continuously enhance and deepen the alliance.