TOKYO (Reuters) - Japanese Prime Minister Yoshihide Suga said on Thursday he had agreed with U.S. President Joe Biden in a phone call to strengthen their bilateral alliance, as China expands its economic and military might. They also agreed to arrange a U.S. visit for Suga as early as possible, Suga told reporters. The White House said the two affirmed the importance of the U.S.-Japan alliance “as the cornerstone of peace and prosperity in a free and open Indo-Pacific.” They two sides said they also reconfirmed that the U.S.-Japan security treaty applied to a group of Japan-controlled East China Sea islets that China claims, called the Senkaku in Japan and Diaoyu in China. Biden reaffirmed too the U.S. commitment to provide “extended deterrence” to Japan, a reference to the U.S. nuclear umbrella covering Japan, the White House said in a statement. The two leaders affirmed the necessity of complete denuclearization of the Korean Peninsula, it added. “We managed to have substantial exchanges,” Suga said. “We agreed to strengthen our alliance firmly by having more phone calls like this.” Shortly after his Senate confirmation on Tuesday, Biden’s new secretary of state, Antony Blinken, spoke to both his South Korean and Japan counterparts and emphasized Biden’s commitment to strengthening the U.S. alliances with both countries. Blinken also stressed the need for continued trilateral cooperation among the allies. Ties between Washington and its two key Northeast Asian allies were bruised under former President Donald Trump, who demanded that both pay more for U.S. troops there and raised questions about their future presence. Biden has said rebuilding relations with allies will be a key priority. Japan-South Korea ties have been strained by a dispute over treatment of Korean women by Japanese forces in World War Two. Last week, Suga called South Korea an important neighbor but said bilateral ties were in a very severe situation.