The United States and Japan "share a concern" about China's activities in the South China Sea, where Beijing has built an air strip and other structures on coral reefs, President Barack Obama said Tuesday.

"The United States and Japan are united in our commitment to freedom of navigation, respect for international law, and the peaceful resolution of disputes without coercion," Obama told a joint White House press conference with Japanese Prime Minister Shinzo Abe.

The alliance between the United States and Japan should not be viewed in China as a threat, Obama said, though he acknowledged mutual concerns over Beijing's actions in the disputed South China Sea.

"We don't think that a strong US-Japan alliance should be seen as a provocation," Obama told the press conference, when asked how Beijing should view their relationship. "As I've said before, we welcome China's peaceful rise."