Japan's finance minister Taro Aso said his country would consider joining China-backed Asian Infrastructure Investment Bank (AIIB) if it proves to be a credible institution complying with generally accepted governance and environmental standards.
"We have been asking to ensure debt sustainability, taking into account its impact on environment and society," Aso was quoted as saying by Reuters.
"We could (consider to join) if these issues are guaranteed. We'll give it careful consideration from diplomatic and economics viewpoints."
If the conditions were met "there could be a chance that we would go inside and discuss. But so far we have not heard any responses," he added.
Aso also wants the bank to have a board of directors to screen and approve individual loan cases.
There were reports that major US allies such as France, Germany and Italy have agreed to join the AIIB, following Britain. In addition, Australia, a key US ally in the Asia Pacific region, is set to decide on joining the international bank next week. China's state-owned Xinhua news agency said South Korea, Switzerland and Luxembourg were also considering joining the AIIB.
The US has not been happy with its key allies' decision, and has highlighted worries about governance and environmental standards. The bank is expected to rival the Manila-based Asian Development Bank and the World Bank in Asia.
Britain has earlier announced its intention to become a founding member of the AIIB – a Chinese-led initiative that is expected to rival the World Bank and the Asian Development Bank in the Asian region.
The move has angered Washington, which said it is wary of Britain's "constant accommodation" of China.
In October 2014, representatives of 21 Asian nations convened in Beijing to inaugurate the AIIB, which is focused on providing funding to infrastructure projects within Asia. The bank was initially capitalised with $50bn (£31bn, €39.5bn), half of which was funded by China.
Britain is the first major Western country to apply to become an AIIB member. It will meet other founding members in March to discuss governance and accountability arrangements.