FILE - In this Wednesday, Oct. 22, 2014 file photo, Federal Reserve Chair Janet Yellen listens during a meeting at the Federal Reserve in Washington. Yellen replaced Ben Bernanke in early 2014. Amid signs that the U.S. economy was growing strongly and unemployment was falling, she and her colleagues brought the Fed’s bond-buying program to an end. (AP Photo/Susan Walsh, File)

The Federal Reserve once again left interest rates unchanged at a range of zero to a quarter of a percentage point, postponing a return to what it calls normal rates and reiterating that “it can be patient” in deciding when to begin raising rates.

The Federal Reserve’s open market committee added that once it begins to raise rates, which most analysts expect will take place around the middle of the year, “economic conditions may, for some time” result in interest rates “below levels the Committee views as normal in the longer run.”

The central bank said that information since its December meeting suggested that “economic activity has been expanding at a solid pace,” more confident sounding than the December statement that pointed to a "moderate pace." It cited strong job gains and lower unemployment rate, a rise in household spending, and increases in business investment. It said that a recovery in the housing sector, however, “remains slow.”

John Canally, an investment strategist and economist for LPL Financial, said that "they see, thus far, only positive spillover from drop in oil prices on economy" in household spending "and no negative" effects, as capital spending remained strong.

Despite a quickening in the rate of economic growth in late 2014, the economy has recently shown signs that it might not sustain that pace, analysts say. Moreover, inflation remains below the central bank’s 2 percent target and unemployment still hovers above the level Fed officials hope to achieve.

The Federal Reserve did not use the phrase "considerable time" to describe how long it would wait before raising rates, but in December Fed chairman Janet Yellen said that being patient meant the central bank would probably wait two meetings, or about six months, before taking action.

Stock and bond markets dropped late in the day despite the lack of movement in the Fed's statement.

The Federal Reserve said that inflation had been low and was “anticipated to decline further in the near term” because of sinking oil prices, but it said that it expected inflation to rise “gradually” toward 2 percent over “the medium term” as the labor market improves and the “transitory effects of lower energy prices and other factors dissipate.” It said that as a result of falling oil prices, inflation had "declined further" below the Fed's target.

Although it did not mention recent events in Europe, the Fed added "international developments" to the list of items it will weigh when trying to decide whether to raise rates. Many analysts believe that Europe’s economic weakness and the European Central Bank’s new program of buying assets would complicate the Federal Reserve’s decision about raising rates without undercutting policy efforts across the Atlantic.

"In Fed-speak, they introduced a variable, which they don’t do very often," said Mark Zandi, chief economist and co-founder of Moody’s Economy.com. "It's a very rare event." Zandi said the "strategic insertion" was "a small change but a very meaningful one" and that it would give the Federal Reserve "more flexibility" in deciding when they will raise rates.

The Fed said in a press release that it was continuing to balance its two mandates, to keep inflation and unemployment rates low. It said that it “continues to see the risks to the outlook for economic activity and the labor market as nearly balanced.”