© Sky News Screen Grab Janet Yellen delivers evidence to Congress

America's top central banker Janet Yellen has delivered a defiant message to president-elect Donald Trump telling US legislators she fully intends to serve out her term until 2018.

Ms Yellen has been subject to speculation that she might step down after Mr Trump was openly critical of her during the election campaign.

But she said she could not see any circumstances in which she could leave her role as chair of the US Federal Reserve early.

Ms Yellen told a congressional hearing: "I was confirmed by the Senate to a four-year term which ends at the end of January 2018

"It is fully my intention to serve out that term."

Mr Trump had charged that Ms Yellen was too political and was keeping interest rates low not to help the economy but to help Democrats retain control of the White House.

But Ms Yellen bridled at the prospect of outside intervention in the Fed's decision-making.

She said there had been "terrible economic outcomes in countries where central banks are subject to political pressure".

Meanwhile, Ms Yellen signalled that the Fed could raise rates "relatively soon" as the US economic picture improves.

Rates in the world's biggest economy have been held close to zero since 2008 and saw a small hike last December, with another widely expected next month.

An increase in the US would have repercussions across global markets.

Ms Yellen's defence of central bank independence comes days after Bank of England governor Mark Carney turned his fire on politicians critical of low rate policy.