Federal Reserve chief Janet Yellen warned Wednesday that the US economy faced risks from tightening domestic financial conditions as well as global economic turmoil.
Expressing concerns that were not nearly as pronounced the last time she spoke publicly in December, Yellen said in prepared testimony to Congress that the outlook for the US economy had become more cloudy.
She made no comment on whether the Fed still expected to continue raising interest rates this year, but her concerns probably lowered the possibility of an increase in its next policy meeting in March.
"Financial conditions in the United States have recently become less supportive of growth, with declines in broad measures of equity prices, higher borrowing rates for riskier borrowers, and a further appreciation of the dollar," she said.
"These developments, if they prove persistent, could weigh on the outlook for economic activity and the labor market."
Yellen said the Fed still expects the US economy to grow at a moderate pace this year, noting that recent employment gains and a tentative pickup in wages "should support the growth of real incomes and therefore consumer spending."
But she said that market turmoil abroad was also buffeting US economic momentum, and could drag down US growth.
The sharp fall in commodity prices -- which she linked in part to "uncertainty" about China's economy and its policies -- threatened to "trigger financial stresses" in commodity-exporting countries and companies.
"Should any of these downside risks materialize, foreign activity and demand for US exports could weaken and financial market conditions could tighten further."
While she gave no hint about the prospects for a rate hike at the mid-March policy meeting, Yellen's warning appeared to reduce that likelihood.
After having increased its benchmark federal funds rate in December for the first time in seven years -- to 0.25-0.50 percent -- Yellen would only say that the Fed "expects that with gradual adjustments in the stance of monetary policy, economic activity will expand at a moderate pace in the coming years."
- US economy's mixed signals -
The key determinants of Fed monetary policy-setting -- inflation and unemployment -- were still giving mixed signals about the strength of the US economy in the short term, according to Yellen's testimony.
Unemployment had fallen to an eight-year low, 4.9 percent, with positive signs in rising wages and a drop in the number of people who want but cannot find full-time work, for example.
Even so, there were still indications that "some slack" remains in the labor market and "there is still room for further sustainable improvement."
Inflation, meanwhile, remains well below the Fed's 2.0 percent target rate, mainly due to the continuing impact of the plunge in oil and other commodity prices. While the Fed expects inflation to move up over the medium term, the weakness suggests the Fed should not move quickly to tighten policy.
Yellen singled out China as a source of some of the major risk to US growth, through a chain of spillover effects from its unclear policy on the yuan currency, or renminbi.
The yuan's recent declines "have intensified uncertainty about China's exchange rate policy and the prospects for its economy," she said.
"This uncertainty led to increased volatility in global financial markets and, against the background of persistent weakness abroad, exacerbated concerns about the outlook for global growth."
In turn, she said, that was contributing to the fall in the prices of oil and other commodities.
"Low commodity prices could trigger financial stresses in commodity-exporting economies" as well as in commodity-producing firms around the world, she said.