The head of the US government's ethics office, who has clashed frequently with President Donald Trump, has resigned.

Walter Shaub, director of the Office of Government Ethics (OGE), had been an outspoken critic of Mr Trump over potential for conflicts of interest involving his business affairs.

Mr Shaub, who also served during the administrations of Barack Obama and George W. Bush, will step down on July 19, six months before the end of bis term.

He said: "In working with the current administration it has become clear to me that we need improvements to the existing ethics programme."

The OGE was established in 1978 to offer guidance to government officials on avoiding conflicts of interest.

In January Mr Shaub was critical of the president's decision not to sell off his global business empire, instead handing over leadership to two of his sons.

At the time Mr Shaub said that did not "meet the standards" set by previous presidents over the last four decades.

Mr Shaub also pressed unsuccessfully for the White House to punish Mr Trump's Counsellor, Kellyanne Conway, for promoting Ivanka Trump's fashion line.

In his resignation letter Mr Schaub said: "The great privilege and honour of my career has been to lead OGE’s staff and the community of ethics officials in the federal executive branch.