Some 30 countries are waiting to join the AIIB and 20 of them have expressed "firm commitment", AIIB President Jin Liqun was quoted as saying by state-run China Daily today.
While the US and Japan have declined to join the bank, Jin said all countries would work together, regardless of the bank membership.
"The door will remain open," Jin said, adding that US and Japanese companies will be treated equally and fairly by the AIIB.
The bank will extend funding to non-Asian countries with "strong economic relations" with the continent and from physical infrastructure projects to sectors including education, healthcare, and urban planning and management, he said.
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The bank plans to holds the first meeting of the board of governors here on June 25.
Beijing-based AIIB was officially established late last year with authorised capital of USD 100 billion. China is the largest shareholder with 26.06 per cent voting shares.
It prioritises investment in energy, power generation, transportation, rural infrastructure, environmental protection and logistics, Jin said.