In a speech prepared for a research conference sponsored by the Federal Reserve Bank of San Francisco, Yellen said most of the Fed officials believed the appropriate time to begin the rate hike has not yet arrived, but they expected that conditions may warrant an increase sometime this year.

　　U.S. economy has recovered from the financial crisis at a slow pace, but there has been significant cumulative progress. The unemployment rate has fallen to 5.5 percent now from 10 percent at its peak; consumer spending remains robust thanks to strong labor market and low energy prices.

　　U.S. Fed to start rate hike this year but at gradual pace: Yellen

　　Yellen expected the real gross domestic product likely to expand faster than its potential in coming quarters, thereby promoting further gains in employment and declines in the unemployment rate.

　　But the central banker also pointed out some headwinds for the economy. Involuntary part-time employment remains high; labor force participation is still lower than expected; wage growth continues to be subdued; dollar appreciation appears to be restraining net exports; low oil prices are prompting a cutback in driving activity; and the recovery in residential construction remains subdued.

　　Inflation, an indicator for Fed in deciding monetary policy, has been below the central bank's 2 percent target for years. The weakness in inflation likely reflects continuing slack in labor and product markets, as well as the sharp decline in energy prices.

　　With labor markets continuing to improve further, the inflation will gradually move up, Yellen said. According to the chairperson, Fed official anticipated that a rather gradual rise in the interest rate will be appropriate over the next few years, as the headwinds holding back growth are likely to continue to abate gradually.

　　Yellen also stressed the pace of rate hike will not follow a set schedule. Instead, the actual path of policy will evolve as economic conditions evolve and policy tightening could speed up, slow down, pause or even reverse course depending on economic developments, she said.

　　The Fed signaled in its March statement that it was moving a step closer toward raising rates, though the central bank cut its economic outlook and slashed its estimate for the federal funds rate, in a sign that it was prepared to move more slowly than the market expected.