China said on Thursday that "domestic reasons" had caused Indonesia to delay joining a new infrastructure bank seen as an attempt by Beijing to rival Western-backed international development banks.

Indonesia, Japan and South Korea were absent when China and 20 other countries agreed in Beijing last month to found the Asian Infrastructure Investment Bank (AIIB), expected to have an initial capital of $50 billion.

But Indonesian finance minister Bambang Brodjonegoro signed an agreement to join the bank on Tuesday, China's official Xinhua news agency reported.

Xinhua cited Brodjonegoro as saying "Indonesia failed to sign the MoU with 21 other countries last month due to domestic political transition" related to its presidential election in July.

Chinese foreign ministry spokesman Hua Chunying said Thursday that "because of domestic reasons, Indonesia failed to join the first batch of funders" for the bank.

She declined to comment on reports that Indonesia had demanded the bank's headquarters be based in Jakarta.

Japanese officials have expressed concern about the new bank's transparency standards, while the United States is reportedly fiercely opposed to the AIIB.

China has maintained it is open to more countries joining, and said it was still in talks with the US and Japan on the issue.