Donald Trump has denied a report that he explored business opportunities in Cuba in the late 1990s, apparently in violation of the US embargo.
The Republican presidential candidate told New Hampshire's NH1 News he "never did business in Cuba".
The tycoon said: "No, I never did anything in Cuba. I never did a deal in Cuba."
Newsweek reported on Thursday that the work was done by a consulting firm called Seven Arrows on behalf of Trump Hotels & Casino Resorts.
The magazine said Mr Trump reimbursed the consulting firm for 68,000 US dollars (£52,000) of business expenses for its Cuba work - even though neither he nor the company had sought a government waiver that would have allowed them to pursue such activities.
Mr Trump criticised Newsweek's reporter, saying he has a "bad reputation".
Hillary Clinton said the report alleging that Mr Trump may have violated the US embargo on communist Cuba was just more evidence that he puts his own interests ahead of the nation's.
The Democratic nominee told reporters aboard her campaign plane that "we have laws in our country," and Mr Trump knew what they were.
She added that "he deliberately flouted" the law and "puts his personal and business interests ahead of the laws and the values and the policies of the United States of America".
Mrs Clinton dismissed Mr Trump's reference to her husband's impeachment - and any other attacks her Republican rival might launch over the couple's personal life.
She said: "He can say whatever he wants to say." And she added that she is going to keep "talking about what I think the American people are interested in".
Earlier in Bedford, New Hampshire, Mr Trump had invoked former President Bill Clinton's impeachment as evidence that the Clintons are "the sordid past," while his presidency would "be the bright and very clean future".
Mr Trump sought to connect Mrs Clinton to her husband's scandal-marked presidency.
He urged supporters to remember that the House in 1998 impeached Mr Clinton on charges of perjury and obstruction of justice. Mr Clinton was acquitted by the Senate.