The International Monetary Fund, citing the consequences of a strong dollar, is downgrading its outlook for the U.S. economy but raising its forecast for Europe and Japan.

The IMF predicted Tuesday that the American economy will grow 3.1 percent this year and next — a performance the fund characterized as "robust."

But the U.S. outlook was down from the IMF's January forecast of 3.6 percent growth in 2015 and 3.3 percent growth in 2016. The American economy advanced 2.4 percent last year.

The IMF forecast that the 18 European countries that use the euro currency collectively will expand 1.5 percent in 2015 and 1.6 percent in 2016, up from a January forecast of 1.2 percent growth this year and 1.4 percent next. The eurozone grew just 0.9 percent last year.

The fund expects Japan to grow 1 percent this year and 1.2 percent next year, versus an earlier forecast of 0.6 percent this year and 0.8 percent in 2016. The Japanese economy shrank 0.1 percent in 2014.

The IMF expects the world economy to grow 3.5 percent in 2015, barely up from 3.4 percent last year and unchanged for its January forecast. It raised the outlook for global economic growth in 2016 to 3.8 percent, up from a January forecast of 3.7 percent.

The international lending agency also left unchanged its prediction that the Chinese economy will grow 6.8 percent this year and 6.3 percent in 2016. That marks a sharp deceleration from last year's 7.4 percent expansion, already the slowest for China in two decades.

But Gian Maria Milesi-Ferretti, the IMF's deputy director for research, told reporters the slowdown in China reflects the country's transition from growth built on often-wasteful investment in factories and real estate to slower but steadier growth built on spending by Chinese consumers. "We think it is a good slowdown for China," he said.

Most of the world's economies are benefiting from sharply lower oil prices. The price of a barrel of oil has plunged to less than $52 a barrel, half what it was a year ago.

Since June 30, the U.S. dollar has climbed 29 percent against the euro and 19 percent against the Japanese yen. A strong dollar makes U.S. products more expensive, giving European and Japanese exporters a price advantage.

Moreover, the Federal Reserve is expected to raise short-term U.S. interest rates this year after keeping them near zero for more than six years. The European Central Bank and the Bank of Japan are moving the opposite direction, pursuing easy money policies meant to stimulate economic growth.

The IMF warned that the U.S. faces long-term challenges, arising from low population growth and unimpressive productivity gains.