New York’s attorney general says he is investigating Republican presidential candidate Donald Trump’s foundation over suspected “impropriety”.
Eric Schneiderman said his office wanted to ensure the foundation is “complying with the laws that govern charities in New York”.
The Trump Foundation has been hit by a number of damaging media stories.
Mr Trump’s team have dismissed Mr Schneiderman, a Democrat, as “a partisan hack.”
The attorney-general has endorsed Mr Trump’s chief opponent, Hillary Clinton, for president.
Mr Trump’s campaign spokesman Jason Miller said Mr Schneiderman had “turned a blind eye to the Clinton Foundation for years”, and called the inquiry “another left-wing hit job designed to distract from Crooked Hillary Clinton’s disastrous week”.
“We have been concerned that the Trump Foundation may have engaged in some impropriety from that point of view,” Mr Schneiderman told CNN.
“And we’ve inquired into it, and we’ve had correspondence with them. I didn’t make a big deal out of it or hold a press conference, but we have been looking into the Trump Foundation to make sure it’s complying with the laws that govern charities in New York.”
US media say Mr Schneiderman’s office has been investigating the Donald J Trump Foundation since at least June when it formally questioned a donation made to a group backing Republican Florida Attorney General Pam Bondi in 2013.
The $25,000 (£19,000, €22,000) payment was made at a time when Mrs Bondi’s office was reportedly considering whether to open a fraud investigation into Trump University.
The fraud investigation never happened, although Mrs Bondi denies the decision was influenced by the donation she received.
Aides to Mr Trump have already admitted the donation was a mistake resulting from clerical errors, according to reports.
The US Justice Department has been asked by Democrats in the House of Representatives to investigate the £25,000 donation to Pam Bondi.
Other newspaper investigations allege the Trump Foundation reported donations that the supposed recipients say they never received, and also spent money on the candidate himself.