BlackRock Inc. said it will start an exchange-traded fund tracking AAA and AA rated sovereign bonds to offer investors “high-quality government debt with global diversification.”

The fund will invest in fixed-rate, local-currency bonds rated AA3 or higher, based on the median of grades from Fitch Ratings, Moody’s Investors Service and Standard & Poor’s, BlackRock said today in an e-mailed statement.

No AAA country will account for more than 20 percent of the fund and no AA rated nation’s debt will be more than 10 percent of investments, BlackRock said.