The Fitch Ratings announced Thursday that it has assigned the Asian Infrastructure Investment Bank (AIIB) its highest possible rating and a stable outlook.

Fitch provided the AIIB with a long-term issuer default rating of AAA and a short-term issuer default rating of F1+, based on the bank's "existing and expected intrinsic strengths."

This was the AIIB's second top-notch credit rating in two weeks. Previously, Moody's Investors Service assigned the AIIB a long-term foreign currency issuer rating of AAA and a short-term foreign currency issuer rating of Prime-1 with a stable outlook.

Fitch said the AIIB has been endowed with a substantial capital base that will support its projected rapid expansion in lending, while its exposure to risk being mitigated by a comprehensive set of policies and high quality governance.

The bank enjoys "an excellent level of liquidity" and should benefit from easy access to capital markets, Fitch said.

"Risks are expected to remain low," Fitch said, expecting the average rating of the loan portfolio to be around 'BB' over the 10-year forecast period.

AIIB treasurer Soren Elbech has said obtaining a rating will pave the way for the bank to issue bonds, but "it will take several months before we are ready."

The Beijing-based AIIB was officially established in December 2015. It prioritizes investment in energy, power generation, transportation, rural infrastructure, environmental protection and logistics in Asia.

The bank now has 80 members or prospective members.