Former president Bill Clinton defended the work of his charitable foundation on Monday, telling supporters that it had "improved millions of lives around the world" but needs to change if his wife, Hillary Clinton, wins the White House.

The former president outlined the Clinton Foundation's accomplishments and planned shift in scope in an email to about 500,000 supporters.

Hours earlier, Republican presidential nominee Donald Trump called the foundation "the most corrupt enterprise in political history", adding, "It must be shut down immediately". He bore down again during a speech later in Akron, Ohio, telling a crowd that if elected, he would have a special prosecutor appointed to investigate the foundation.