Federal Agency Security is a debt instrument issued by an agency of the federal government, such as the Federal National Mortgage Association or the Federal Farm Credit Bank. Though not obligations of the U.S. Treasury, these securities are sponsored by the government and have high credit ratings.
Government Agency Securities are securities issued by U.S. government agencies like the Federal Home Loan Bank, the Federal Farm Credit Bank, or the Federal National Mortgage Association. These securities, while highly rated, are not backed by the full faith and credit of the U.S. government.
Sovereign bonds are debt securities issued by a national government, with a promise to pay periodic interest payments and to repay the face value on the maturity date.