US President Donald Trump on Wednesday signaled new action against left-wing groups following the assassination of right-wing political activist Charlie Kirk, targeting the anti-fascist antifa movement as a "terrorist organization," Reuters reports.

Trump said on Truth Social that he was "designating" the movement as a terrorist organization. "I will also be strongly recommending that those funding ANTIFA be thoroughly investigated in accordance with the highest legal standards and practices," Trump wrote.

It was not clear what legal weight Trump's proclamation carried. Antifa is a loosely organized ideological movement without a clear leadership structure or hierarchy, experts said.

Trump and senior officials have repeatedly blamed left-wing groups for creating an atmosphere of hostility towards conservatives before Kirk's assassination.

Critics say that Trump is using Kirk's assassination as a pretext to crack down on political opponents.

Trump initially floated the idea of such a designation for antifa in 2020 amid violent nationwide protests following the police killing of George Floyd in Minneapolis.

At the time, legal experts said such a step lacked a basis in law, would be hard to execute, and raised free-speech concerns, given that subscription to an ideology is not generally considered criminal.