China has vowed an open and inclusive attitude and welcomes interested countries to participate in its planned Asian Infrastructure Investment Bank (AIIB), the foreign ministry said on Monday.

"The AIIB will draw upon the sound practices of existing multilateral development banks and set up a high standard and feasible safeguard policies," Hong Lei, a foreign ministry spokesperson, told reporters at a Monday briefing.

The response came after the US reportedly proposed cooperation between the China-led bank with US-backed institutions.

"The US would welcome new multilateral institutions that strengthen the international financial architecture," Nathan Sheets, US Treasury undersecretary for international affairs, was quoted as saying by the Wall Street Journal on Sunday.

"Co-financing projects with existing institutions like the World Bank or the Asian Development Bank would help ensure that high-quality, time-tested standards are maintained," Sheets said, adding that the AIIB would help meet major infrastructure-investment gaps if the AIIB could adopt the same standards.

The US had taken a negative attitude toward the $50 billion bank initiative proposed by China in October 2014 to fund infrastructure projects in Asia, according to previous media reports.

"The softened attitude toward the AIIB shows that the US is becoming pragmatic," Gong Jiong, an associate professor at the Beijing-based University of International Business and Economics, told the Global Times on Monday.

Several European countries - including the UK, Switzerland and Luxemburg - have signed up as AIIB founding members since March 18.

Japanese Finance Minister Taro Aso signaled for the first time on Friday that Tokyo could be part of the AIIB if the new bank can guarantee a credible mechanism for providing loans, but top government spokesman Yoshihide Suga said the government remains cautious over his country's participation, Reuters reported.

The bank will have more than 35 prospective founding members by the deadline, Jin Liqun, secretary-general of the Multilateral Interim Secretariat for Establishing the AIIB, said at the China Development Forum held on Sunday.

"The US is aware that it cannot stop others from participating, which is beneficial to the AIIB. With the greater participation of financial powers like Switzerland, the AIIB will have more credibility to facilitate bond sales in the future," Ding Yifan, a research fellow at the Development Research Center of the State Council, told the Global Times on Monday.

"However, it may be difficult for the US to join, considering that its Republican-dominated Congress might not approve its participation," he noted.

Instead of being a rival, Finance Minister Lou Jiwei emphasized on Friday that the AIIB will complement other financial institutions.

World Bank Managing Director Sri Mulyani Indrawati said in an interview with the Xinhua News Agency on Sunday that the World Bank and the AIIB are working "very closely" in the beginning and looking at the AIIB's setting, principles and framework.

Other leading global lenders, such as the International Monetary Fund (IMF), have also said they welcome collaboration with the new bank to fill Asia's infrastructure gap.

In a statement issued after she met Premier Li Keqiang in Beijing on Monday, IMF head Christine Lagarde hailed Beijing's "impressive efforts" to reform and said she welcomes China's creation of a new infrastructure bank.

Lagarde also said earlier at the China Development Forum that IMF would cooperate with the new bank.

Lou insisted on Sunday that some current mechanisms and principles proposed by the West may not be the best practices and China will take the requests of developing countries into consideration in the future.

"The AIIB can work with other institutions in various ways including cross-holding and project development, as there will be some overlapping of project operations. But we are in no position to accept supervision from others as we are in a peer relationship with other multinational institutions," Huang Wei, deputy director of the Institute of World Economics and Politics at the Chinese Academy of Social Sciences, told the Global Times on Monday.