Total foreign holdings rose 0.6 percent to $6.01 trillion, up from $5.98 trillion in May, the Treasury Department said Friday in its monthly report.
The increase came despite the fact that the two biggest foreign owners of Treasury securities reduced their holdings slightly.
China, the top foreign buyer of U.S. Treasury debt, trimmed its holdings by 0.2 percent to $1.27 trillion after a 0.6 percent increase in May. Japan, the second-biggest foreign buyer, saw its holdings slip a slight $600 million to $1.22 trillion.
Belgium, Brazil and Taiwan were among the countries increasing their holdings.
Foreign central banks are big holders of U.S. Treasuries, which are viewed as one of the world's safest investments. In June, foreign government holdings of Treasury debt totaled $4.1 trillion, two-thirds of the total foreign holdings.
Foreign demand for Treasury debt is expected to remain strong this year, helped by a congressional agreement to avoid a new fight over the U.S. debt ceiling until March 2015.
A standoff in August 2011 rattled financial markets and the political gridlock led the credit rating firm Standard & Poor's to downgrade its AAA rating of U.S. debt for the first time in history.