WASHINGTON (Reuters) - U.S. Treasury Secretary Steven Mnuchin on Thursday announced further cash management measures to avoid a U.S. default.


In a letter to House of Representatives Speaker Paul Ryan, Mnuchin said that Treasury would no longer be able to fully invest in three retirement and investment funds for federal workers.


They are the Civil Service Retirement and Disability Fund, the Postal Service Retiree Health Benefits Fund, and the Government Securities Investment Fund of the Federal Employees' Retirement System, according to the letter.


All the funds would be made whole once the debt limit is increased, Mnuchin said. "Federal retirees and employees will be unaffected by these actions," he added.


A suspension of the debt limit by Congress, which had allowed normal borrowing to continue, expired on Wednesday.


The United States is one of only a few nations where the legislature must approve periodic increases in the legal limit on how much money the federal government can borrow.

(Reporting by Lindsay Dunsmuir; Editing by Chizu Nomiyama and Leslie Adler)