Leaders of the Group of Seven industrial nations discussed a new Chinese-led Asian investment bank at their summit on Sunday, with Prime Minister Shinzo Abe underlining the need to address issues like corruption, his spokesman said.

While 57 countries, including G-7 members Britain, Germany and France, have joined the Asian Infrastructure Investment Bank (AIIB) as founding members, Japan and the United States have stayed out of a venture seen as a rival to the U.S.-dominated World Bank and Japan-led Asian Development Bank (ADB).

Tokyo is, however, keeping its options open.

Abe's spokesman, Yasuhisa Kawamura, told reporters at the G-7 summit in the Bavarian Alps that Japan would not say whether or not it would join the bank until China had tackled concerns about human rights, debt sustainability, environmental protection and governance.

"Whether the AIIB would clear those elements is quite important for us. So unless those questions (are) cleared, Japan wouldn't position (itself on) whether to join or not," he said. "(Abe) took note of the importance of the corruptions to be addressed."

Tokyo has asked the Chinese authorities to clarify those issues but Beijing has not yet straightened them out, he said, adding that Japan would continue to talk to China about this.

Kawamura said Finance Minister Taro Aso had mentioned recently that cooperation between the ADB and the AIIB might be possible in the future if Beijing tackled Tokyo's concerns.

He also said that German Chancellor Angela Merkel had said that next year, when Japan has the presidency of the G-7, the issue needed to be discussed continually.