US President Donald Trump said that conservative economic commentator Stephen Moore has withdrawn from consideration to become a member of the Federal Reserve Board, the president's second candidate to pull out.

"Steve Moore, a great pro-growth economist and a truly fine person, has decided to withdraw from the Fed process," Mr Trump said on Twitter, moments after Mr Moore told Bloomberg and The Wall Street Journal that he would stay in the race.

Mr Trump's other candidate, businessman and long-shot presidential candidate Herman Cain, also pulled out of the race to fill one of two remaining openings on the central bank board.

Mr Trump has repeatedly ignored norms designed to protect the independent Fed from political influence, which could undermine its credibility, lambasting the central bank for raising interest rates and even this week calling for a drastic cut.

In that atmosphere, his nominations of Mr Moore and Mr Cain were viewed by some as an attempt to bring pressure from the inside. They also were criticised for their lack of qualifications, including by Republicans in the Senate.

Five of the 53 Republicans in the 100-member chamber told AFP there were serious problems with Mr Moore's candidacy, adding to concerns that at least two other Republican senators had shared with reporters in recent days.

Senator Joni Ernst of Iowa hardened her opposition after the emergence of articles and speeches by Mr Moore over the years, some of which have been criticised as sexist or trafficking in racism.

Mr Moore, a 59-year-old economic and political commentator, advised Mr Trump when he was running for president and has publicly expressed his opposition to raising interest rates.

He gave two interviews published within an hour of Mr Trump's tweet saying he was staying in the race, and that a White House official had encouraged him to remain.

"I sure am," Mr Moore told Bloomberg when asked if he would persist in seeking a Fed seat. "I'm not too concerned about this."

Mr Trump said on Twitter that he asked Mr Moore "to work with me toward future economic growth in our Country."

The Fed has a seven-member board, but has had openings for many months.

Mr Trump has named three current Fed members to the board, including Vice Chairman Richard Clarida, and also promoted Jerome Powell to his current post as board chair.

US Fed keeps rates unchanged

The news comes after the US Federal Reserve last night decided to keep its benchmark interest rate unchanged amid mixed signals about the direction of the US economy. 

But Fed Chair Jerome Powell seemed to dampen down growing expectations that officials might lean towards a rate cut, something President Trump has demanded of the bank. 

After raising the key lending rate four times last year, the Fed voted unanimously to keep it in a range of 2.25-2.5%. 

Conflicting economic data has complicated the Fed's decision-making. 

While the Fed noted the continued "strong labour market" and "solid" gains in economic activity, it also highlighted a slowdown in investment by businesses and households as well as weak inflation.

This has fallen further below the Fed's 2% target to around 1.6%. 

Asked whether there was a case building to cut rates to push the price measure closer to the target, Powell told reporters factors that "appear to be transient or idiosyncratic," such as clothing and airfares, are likely behind the low inflation rate.

He added that US central bankers are "comfortable" about policy at the moment.

"We think that our policy stance is appropriate at the moment. And we don't see a strong case for moving in either direction," he said, but added policymakers will be "watching inflation carefully." 

In his latest Twitter attack, Mr Trump had slammed the Fed for "incessantly" raising interest rates despite low inflation, and called on officials to cut the rate by a full percentage point.

Those attacks have left the institution open to concerns it might bow to political pressure. But Powell dismissed those fears as he has done repeatedly. 

"We don't think about short term political considerations, we don't discuss them and we don't consider them in making our decisions one way or the other," he said. 

The statement by the rate-setting Federal Open Market Committee offered just a few key changes of language. 

Data since the March policy meeting show "the labour market remains strong and that economic activity rose at a solid rate," the FOMC said, somewhat more optimistic than the prior statement that noted slowing activity.

But the FOMC also noted that growth in household spending and business fixed investment had "slowed in the first quarter," and that key inflation measures "have declined and are running below 2%."