A U.S. federal grand jury has approved the first charges in an investigation led by special counsel Robert Mueller, according to multiple media reports.

CNN and NBC report that the charges were approved Friday and remain sealed under orders from a federal judge. Details of the charges – including who they are against – have not been made public.

Sources told CNN that anyone charged could be arrested as soon as Monday.

Neither U.S. President Donald Trump nor the White House has responded to the reports.

Mueller, the former director of the FBI, was tasked in May with leading an investigation into Russian meddling in the 2016 U.S. election and possible collusion with the Trump campaign.

National security lawyer Bradley Moss told CTV News that the reported developments could be evidence that “Mr. Mueller has found something.”

“Not necessarily the whole picture, but he’s found the first piece of the puzzle that will help him eventually put together … what the nature of the collusion, if any, actually was,” Moss said.

“This could be -- and I emphasize could, because we don’t know, it’s a long way off -- but this could be the beginning of the end in terms of what ultimately takes down this administration.”

Trump has repeatedly denied any collusion. Last week, he called the allegations “an excuse” from the Democrats for losing the election.

With a report from CTV's Washington Bureau Correspondent Richard Madan