The foundation established by Bill and Hillary Clinton is at the centre of fresh controversy after it was revealed that half of the people who met her when she was secretary of state gave money to the organisation.

In the latest twist to a saga that has seen Republican candidate Donald Trump call for an independent investigation of the foundation, an analysis by the Associated Press has revealed that 50 per cent of private individuals who got to see her - at least 85 of 154 - donated money either personally or through a company. Combined, the 85 donors contributed as much as $156m.

The Clinton Foundation was established in 1997 by former president Bill Clinton improving global health, increasing opportunity for women and girls, and reducing childhood obesity. Yet as Ms Clinton has made her bid for the White House, the foundation has been the target of allegations of that it accepted donations in exchange for political access. The foundation has raised more than $2bn in donations and currently has 2,000 employees.

Mr Trump has been at front of those alleging impropriety.

“Hillary Clinton is totally unfit to hold public office,” he said at a rally Tuesday night in Austin, Texas. “It is impossible to figure out where the Clinton Foundation ends and the State Department begins. It is now abundantly clear that the Clintons set up a business to profit from public office.”

The Clintons have both denied that there has ever being anything like the process of “pay-for-play” that Mr Trump has alleged. Yet as with many things relating to the couple’s political endeavours, the optics of the arrangement are not good.

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Aware of how things may look bad - while insisting nothing unethical has transpired - Mr Clinton said that if his wife were to win, he would step down from the foundation’s board and stop all fundraising for it.

The foundation has said would also accept donations only from US citizens and what it described as independent philanthropies, while no longer taking gifts from foreign groups, US companies or corporate charities.

The AP analysis found that among those granted time with Ms Clinton included Muhammad Yunus, an internationally known economist who asked for her help as the Bangladesh government pressured him to resign from a nonprofit bank he ran, a Wall Street executive who sought her help with a visa problem, and Estee Lauder executives who were listed as meeting with Ms Clinton while her department worked with the firm's corporate charity to counter gender-based violence in South Africa.

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The meetings between the Democratic presidential nominee and foundation donors do not appear to violate legal agreements Ms Clinton and her husband signed before she joined the State Department in 2009.

But it said the frequency of the overlaps shows the intermingling of access and donations, and fuels perceptions that giving the foundation money was a price of admission for face time with Ms Clinton.

Brian Fallon, a spokesman for Ms Clinton, said the nature of some of her meetings was being misrepresented.