Defense Minister Taro Kono’s weekend trip to Guam to meet his U.S. counterpart came as Japan faces a double-barreled challenge of a leadership transition amid the COVID-19 pandemic and China's growing maritime assertiveness.

The visit came just a day after Prime Minister Shinzo Abe shocked the nation by announcing his intention to resign from his post after a record-setting term in office that saw him rebuild frayed ties with China while also bolstering the Japan-U.S. alliance.

Kono and U.S. Defense Secretary Mark Esper on Saturday vowed to keep China in check in both the disputed South China Sea and the East China Sea, home to the Japanese-controlled Senkaku Islands, which are also claimed by Beijing.