Donald Trump has been accused by New York state prosecutors of illegally using his charitable foundation as a personal piggy bank, improperly tapping its funds to support his presidential campaign and settle legal claims against his businesses.

In a lawsuit filed by the state’s attorney-general on Mr Trump’s 72nd birthday, the president was accused of engaging in a pattern of “persistent illegal conduct” over more than a decade and running the Donald J. Trump Foundation “according to his whim, rather than the law”.

“The Trump Foundation was little more than a cheque book for payments from Mr Trump or his businesses to non-profits, regardless of their purpose or legality,” said Barbara Underwood in a statement. She became New York’s attorney-general in May after Eric Schneiderman resigned following sexual harassment claims.