Chinese state media took a victory lap on Wednesday, gloating over the decision of major European powers to join a Beijing-backed multinational lender that the United States perceives as a threat to the Washington-led World Bank.

"Welcome Germany! Welcome France! Welcome Italy!" said a commentary in the official Xinhua news agency, describing the United States as "petulant and cynical".

Berlin, Paris and Rome said in a joint statement Tuesday that they want "to become founding members of the Asian Infrastructure Investment Bank (AIIB)", after Britain last week announced ambitions to be the first major Western country to join -- drawing a rare rebuke from close ally Washington.

Calling the triple decision a "brave yet rational move", Xinhua said it contained a stark message for the US.

Washington was "trying to forge an anti-AIIB front" among its allies, the commentary said, but "sour grapes over the AIIB makes America look isolated and hypocritical".

"As more and more Western countries mull over joining the China-led lending body, the US will feel lonelier if it continues to be a holdout," it added. "So Washington, what are you waiting for?"

China touts the $50 billion institution as a tool for financing regional development alongside other lenders such as the World Bank and the Japan-led, Manila-based Asian Development Bank.

Beijing's finance ministry welcomed the German, French and Italian announcements, saying it would "consult" the bank's existing prospective founder countries and the trio would join them within a fortnight if their applications were "approved smoothly".

- 'Open and inclusive' -

Chinese foreign ministry spokesman Hong Lei said Wednesday that the AIIB was "an open and inclusive institution" ready to receive further applications, adding: "Its door is always open."

US Treasury Secretary Jacob Lew did not dress down Berlin, Paris and Rome but questioned whether the AIIB would "adhere to the kind of high standards" of other global institutions in comments before Congress.

The state-run China Daily insisted in an editorial that even though the new bank was proposed by and headquartered in Beijing, that "does not mean it is Chinese, or an instrument of Chinese soft power".

It sought to take the moral high ground over the latest developments.

"US obstructionism has been less than effective this time because it has failed to see that Washington and Beijing have no reason to stand against each other on a matter such as this," it added.

"Washington has been urging Beijing to act like a 'responsible' power. The AIIB is Beijing's latest answer to that call."

The Global Times newspaper, affiliated with Communist Party mouthpiece People's Daily, portrayed the European decisions as a clear victory for Beijing.

"Many analysts believe that the current situation proves the US lacks the ability to contain a rising China," it said in an editorial.

"As China has won the race around the AIIB, it has also gained some important rights for the future."

But it also warned against carrying anti-Washington taunts too far.

"An approach that sets the US as an adversary is contrary to China's doctrine."