The decline in oil and stocks during the first two months of the year, as well as a slowdown in China had pushed back or reduced expectations for an interest rate hike by the Fed. That prompted investors to add U.S. Treasurys to their portfolios.

Benchmark interest rates at the beginning of February were at 1.8480 percent. By the end of the month, U.S. 10-year yields had declined as low as 1.6470 percent.

Overseas investors bought $9.9 billion in Treasury debt in February, data showed, after selling $50.4 billion the previous month. Foreign investors have sold Treasurys in five of the last eight months.

Private investors purchased $60.2 billion in U.S. government debt for the month of February, offsetting sales by foreign official institutions, mainly central banks, of $48.3 billion.

China's holdings of U.S. Treasurys increased in February to $1.252 trillion from $1.238 trillion. The world's second largest economy remains the largest holder of U.S. Treasurys.

Japan, the second-largest U.S. Treasury debt holder, posted higher U.S. government debt holdings $1.133 trillion from $1.124 trillion in January. It was Japan's second increase in eight months.

Overall, foreign central bank holdings of U.S. Treasurys grew to $6.236 trillion in February, from $6.183 trillion the previous month.

Data also showed that foreigners bought $72 billion in long-term U.S. assets, after sales of $11.9 billion in January. Including shorter-dated securities, overseas investors bought $33.5 billion in February, after buying a revised $116.6 billion the previous month.

With U.S. stocks under pressure in February, foreign investors sold $11.1 billion in stocks during the month, after buying $4.6 billion in January. Private investors led the way in dumping U.S. stocks to the tune of $12.4 billion in February, even as foreign official institutions bought $1.2 billion the same month.