Iran had been accepted as a founding member of the BRICS-led Asian Infrastructure Investment Bank (AIIB), Chinese state news agency reported late on Tuesday.
Xinhua added that the UAE had also been accepted.
The AIIB was seen as a potential rival to established lenders the World Bank and Asian Investment Bank, which were dominated by the US and Japan.
The decision was made by existing members, including China, Britain, France, India and Italy, it added.
China and Iran had close diplomatic, economic, trade and energy ties.
Meanwhile, Japan had indicated that it remained interested in joining the China-proposed Asian Infrastructure Investment Bank (AIIB) with local media reporting Wednesday that the government had earmarked $1.5 billion as its contribution.
The government had prepared a draft document on the possibility of its joining the AIIB, which was scheduled for launch by the end of the year, with the document suggesting that Japan still had certain issues as regards the governance of the bank.
However, sources close to Japanese prime minister Shinzo Abe today said the PM was strongly in favour of Japan joining the China-led initiative and was currently further evaluating the prospect.
According to sources familiar with the matter, Japan's initial investment of $1.5 billion was based on an assumption that of the $50 billion dollars initial capitalisation of the bank, $10 billion would come from direct investments from potential members.
Japan's investment was calculated considering the nominal gross domestic product of the bank's potential participants with Asian economies contributing 75 per cent of the payments, the sources said. The sources further added non-Asian economies would contribute 25 per cent of the payments.
Japan, which had China as its biggest trade partner, hoped that its joining the AIIB could help improve ties between Tokyo and Beijing, which had soured of late owing to issues of territory and history.