Moody’s said Friday that it believes Royal Bank of Canada’s (TSX:RY) covered bonds will maintain their Aaa ratings even if the bank’s senior unsecured rating is lowered.

“Moody’s believes that RBC, if downgraded, will support its covered bond program by committing sufficient additional collateral to maintain the Aaa ratings of the covered bonds,” the agency said.

“RBC’s management informed Moody’s that it is committed to maintain the Aaa rating of the covered bonds by lowering the maximum asset percentage to 93% if necessary.”

The debt rating agency placed Royal Bank under review for a possible downgrade earlier this week, but did not put the bank’s covered bond ratings on review.

Covered bonds are debt instruments that are secured by a pool of high-quality assets such as mortgages.

The Royal Bank has said it does not believe it deserves to be among a group of the world’s largest banks whose credit ratings have been placed under review by Moody’s because of their exposure to the global capital markets business.

Besides the Royal Bank, other banks in line for possible downgrades include Citigroup, Bank of America, Goldman Sachs, JP Morgan Chase and Morgan Stanley.

The credit ratings agency, which also extended ongoing reviews for downgrades on 11 companies, said the review could result in a downgrade of the Royal Bank by up to two notches, but cautioned that a final determination had not been made.

The review follows a move by Moody’s to downgrade Royal Bank to Aa1 from Aaa in December 2010 due to the bank’s capital markets exposure.

DBRS rates Royal Bank an AA, while S&P rates the bank AA-.

Royal Bank earned a record $6.7 billion from its continuing operations last year, while total net income dropped to $4.85 billion from $5.22 billion in 2010 due to a writedown related to the sale of its U.S. retail banking operations. Revenue grew to $27.43 billion from $26.08 billion.

It is the country’s largest bank by assets and market capitalization and has 77,000 employees serving more than 18 million clients. The bank has operations across North America and in 52 other countries.