Defense ministers from Asia and other regions gathered in Singapore for a security forum that started Friday, with heightened tensions between the United States and China, as well as North Korea's weapons program, expected to top the agenda after Beijing declined a bilateral meeting of the two countries' defense chiefs.

During the three-day meeting, U.S. Defense Secretary Lloyd Austin and China's Defense Minister Li Shangfu will deliver speeches, according to the London-based International Institute for Strategic Studies that sponsors the annual Shangri-La Dialogue.

Among the issues to be discussed are China's assertive territorial claims in the South China Sea, the Taiwan issue, North Korea's nuclear and missile development and Russia's war on Ukraine.

Chinese Defense Minister Li Shangfu (L) shakes hands with Singapore Defense Minister Ng Eng Hen in Singapore, on June 1, 2023. (AP/Kyodo)

Aside from the main conference, many bilateral meetings are expected to take place on the sidelines. China rejected Austin's request to meet one-on-one with Li, a Pentagon official said Monday, in the latest development that reflects the problematic U.S.-China relationship.

Li, who became defense minister in March, was sanctioned by the United States in 2018 over Chinese weapons purchases from Russia.

Defense ministers of Japan, the United States, Australia and the Philippines are planning to hold their first-ever quadrilateral talks on the fringes of the forum, diplomatic sources told Kyodo News.

Japan and the United States will hold a trilateral meeting with South Korea and another one with Australia, the Japanese Defense Ministry said Thursday.

The meetings will take place as Tokyo and Washington are bolstering security cooperation with Canberra, Manila and Seoul in the face of China's growing assertiveness in the region and increased military threats posed by North Korea.

Pyongyang has vowed to launch a military reconnaissance satellite after its first attempt at doing so by apparently using sanctions-defying ballistic technology failed Wednesday.

The war in Ukraine, which has raged for over 15 months, will be discussed at the security forum, with Ukrainian Defense Minister Oleksii Reznikov also joining.

Ukraine's President Volodymyr Zelenskyy addressed the conference remotely last year.

Nearly 600 delegates from more than 40 nations, including some European countries, attend the forum in person this year, according to the organizer. The conference has been held annually in Singapore since 2002 but was canceled in 2020 and 2021 due to the coronavirus pandemic.