The U.S. should not take low borrowing costs for granted, said John Lipsky, the International Monetary Fund’s former no. 2 official and now a special adviser to the IMF chief.

While the U.S. and Japan enjoy “extremely low” bond yields even with high debt burdens, the debt crisis in the euro region showed investors can suddenly turn their back on a country, Lipsky said in a speech in Washington Thursday. The best way to reassure them is to devise and publish plans on how governments aim to reduce budget deficits and debt over the medium term, he said.

“Markets can change their minds, and when they do change their minds, they tend to do it in a hurry,” said Lipsky, whose term as first deputy managing director ended Aug. 31. “To ignore these big problems, even in the biggest economies, would be a real mistake.”

Congress, which last month agreed to raise the U.S. debt ceiling, has yet to agree on the specifics of a 10-year deficit- cutting plan. At the same time, treasuries posted the biggest monthly gain since December 2008 as investors ignored the first- ever rating downgrade of the U.S. and sought a refuge in the safest securities amid signs of slowing global growth.

Lipsky spoke at the presentation of a book by IMF economists that studies previous fiscal adjustment plans in advanced economies.