WASHINGTON (AFP) - Federal Reserve policymakers were split at their last meeting on when to raise ultra-low interest rates, with liftoff ranging from June to 2016, minutes to the meeting showed Wednesday.

"Several" participants at the Federal Open Market Committee meeting on March 17 and 18 judged that the economic conditions and outlook would be favourable for a rate hike later in the year.

Others deemed the circumstances would be right later in the year, while "a couple" of officials said liftoff would remain unlikely until 2016, the FOMC minutes said.

At the meeting, the Fed left its key federal funds rate unchanged near zero, where it has been pegged since late 2008.

It dropped from its policy statement a line used previously saying it will remain "patient" before acting - a signal that a rate hike could come as early as June.

But the FOMC said it expects it will be appropriate to raise the rate when it had seen further improvement in the labour market and is "reasonably confident" that currently weak inflation will move back to its 2 per cent target over the medium term.

Participants at the March meeting expressed "a range of views" with regard to the outlook for inflation.

"It was noted that there were no simple criteria for such a judgment" and that "the normalisation process could be initiated prior to seeing increases in core price inflation or wage inflation," the minutes said.

"Further improvement in the labor market, a stabilisation of energy prices, and a leveling out of the foreign exchange value of the dollar were all seen as helpful in establishing confidence that inflation would turn up."