Treasury had spent about $225 billion on purchases of mortgage debt over 16 months before it began selling the securities last year, the Journal said.

The government last week sold the last of the bonds, liquidating the Treasury's ownership of debt backed by Fannie Mae (FNMA.OB) and Freddie Mac (FMCC.OB), the newspaper said.

Investors were worried about the movement of asset prices in the event of curtailment of government support.

"We said if we thought there was any stress in the market around this, we would pull back," Mary Miller, the Treasury's assistant secretary for financial markets, told the Journal.

"We frankly never saw that and just continued," she added.

The mortgage purchases were one of the tools employed by the U.S. government to prop up the financial system at the height of the credit crisis. Separately, the Federal Reserve had also rolled out its own programs to achieve economic stability.

Treasury Department could not immediately be reached for comment by Reuters outside regular U.S. business hours.

(Reporting by Sakthi Prasad in Bangalore; Editing by Ramya Venugopal)

• A Permanent Economic Emergency