President Barack Obama confirmed on Thursday that Donald Trump will get national security briefings ahead of the November election, but he warned the Republican candidate, whom he has called "unfit" for office, that information from the meetings must be kept secret.

Obama, a Democrat who has endorsed his former Secretary of State Hillary Clinton in the 2016 White House race, has made clear his dismay over Trump, a New York businessman who has proposed temporarily banning Muslims from entering the United States and building a wall on the U.S. border with Mexico.

On Tuesday Obama questioned why leading Republicans have not withdrawn their support for their presidential nominee. On Thursday he dismissed as ridiculous Trump's claims that the election may be rigged.