US President Donald Trump signed an executive order on Thursday to ensure that American colleges and universities protect free speech on their campuses.

"Even as universities have received billions and billions of dollars from taxpayers, many have become increasingly hostile to free speech and the first amendment," Trump said. "Taxpayer dollars should not subsidize anti-first amendment institutions and that's exactly what they are, anti-first amendment. Universities that want taxpayer dollars should promote free speech."

Trump said there have been incidents at universities throughout the US where free speech was restricted.

The executive order is aimed at preventing action against conservative students protesting at US colleges and universities. Trump was compelled to issue the order after a student at the University of California at Berkeley was punched in the face last month for supporting the president and conservative causes.

A week after the incident, Trump brought the student, Hayden Williams, on stage with him during a speech at the Conservative Political Action Conference as he announced his intent to sign an executive order to protect free speech on college campuses.