By Linda Sieg and Tetsushi Kajimoto
TOKYO (Reuters) - The secretary-general of Japan's ruling party said on Tuesday he will attend China's New Silk Road summit in May, a sign Prime Minister Shinzo Abe wants to improve ties with Beijing amid tensions over North Korea's missile and nuclear programs.
But an adviser to Abe said Tokyo remained cautious about the China-backed Asian Infrastructure Investment Bank (AIIB), created at least in part as a way to fund the Silk Road plan.
"Given the international situation starting with North Korea, mutual understanding between Japan and China is vital," Liberal Democratic Party (LDP) Secretary General Toshihiro Nikai was quoted by Jiji news agency telling a news conference, adding he would attend the May 14-15 China summit.
Speaking in Beijing, Chinese Foreign Ministry spokesman Geng Suang confirmed the attendance. Geng gave no other details.
Concerns have grown that a sixth North Korean nuclear test could be imminent and that the test, or another long-range missile launch, could occur around the 85th anniversary of the foundation of the North's Korean People's Army on Tuesday.
North Korea conducted a big live-fire exercise on Tuesday to mark the foundation of its military, media reported, in defiance of U.S. warnings against such action.
Nikai, a ruling party heavyweight and second to Abe in the party, is known for his close ties to China.
Japan's ties with China have long been plagued by the bitter legacy of World War Two and mistrust over present-day regional rivalry. But Japan, like the United States and South Korea, wants Beijing, North Korea's main backer, to pressure Pyongyang to abandon its missile and nuclear programs.
Japan's trade minister, Hiroshige Seko, is also considering attending after receiving an invitation, Chief Cabinet Secretary Yoshihide Suga told a news conference, while Sadayuki Sakakibara, chairman of business lobby Keidanren will also go.
Chinese Foreign Minister Wang Yi, in announcing a list of those attending the summit earlier this month, which includes many Asia leaders, did not mention officials from Japan, South Korea or North Korea.
Chinese President Xi Jinping has championed the "One Belt, One Road" initiative to build a new Silk Road linking Asia, Africa and Europe, investing billions of dollars in infrastructure projects.
Japan, following Washington's lead under then-U.S. President Barack Obama, did not join the AIIB, partly from concern it was a vehicle to boost China's regional clout and a potential rival of the Asian Development Bank (ADB), the Manila-based institution dominated by Japan and the United States.
In May 2016, the AIIB and ADB signed an agreement setting the stage for joint financing projects.
"We remain cautious about AIIB and need to examine its transparency even more closely, since China plays a dominant role in its governance," Abe adviser Masahiko Shibayama, told Reuters.
(Additional reporting by Michael Martina in BEIJING; Editing by Michael Perry and Clarence Fernandez)