LONDON (Reuters) - Britain said it had become the first Group of Seven economy to sign off on the rules of a China-backed development bank for Asia, which is seen by the United States as an unwelcome rival to Western-led institutions such as the World Bank.

“This caps a tremendous year for the UK’s economic relations with Asia, the fastest growing region of the world economy,” British Chancellor George Osborne said in a statement issued on Thursday.

Britain was the first non-Asian country as well as the first from the G7 to ratify the Asian Infrastructure Investment Bank’s articles of agreement, he said.

Britain was the first Western nation to join the AIIB earlier this year, prompting other countries to sign up, despite Washington’s concerns.

The British government has prioritised developing economic ties with China and welcomed Chinese President Xi Jinping on a state visit in October. But domestic critics said it was placing short-term financial gains above human rights and Britain’s longer-term security interests.

The AIIB was launched in Beijing last year to spur transportation, energy, telecommunication and other investment. The United States has previously expressed concerns about whether the AIIB would have sufficiently high standards on governance and environmental and social safeguards.