US President Donald Trump has called for billionaire George Soros and his son to face criminal charges over unfounded claims that the family is behind "violent protests" around the country.

Trump did not specify what had prompted his morning outburst, but it comes as his administration pursues multiple criminal investigations against his perceived enemies.

"George Soros, and his wonderful Radical Left son, should be charged with RICO because of their support of Violent Protests, and much more," the president wrote on his Truth Social platform on Wednesday, referring to a law against taking part in a criminal organisation.

Street protests broke out in Los Angeles in June in response to a ramp-up of immigration raids.

Trump used the demonstrations as justification to deploy the National Guard and Marines into the Democratic-run city.

Fact-checkers, including AFP, debunked several images which circulated online at the time, claiming to show that groups backed by the Soros family had strategically placed bricks to hurl at police.

Joe Biden awarded the elder Soros a presidential Medal of Freedom in January shortly before Trump took office, citing Soros's support for "organisations, and projects across the world that strengthen democracy, human rights, education and social justice."