US PRESIDENT Donald Trump is escalating threats to crack down on what he describes as the “radical left” following Charlie Kirk’s assassination, raising fears that his administration is trying to exploit outrage over the far-right activist’s killing to suppress political opposition.

Without establishing any link to last week’s shooting, the Republican president and members of his administration have discussed classifying some groups as domestic terrorists, ordering racketeering investigations and revoking tax-exempt status for progressive non-profit organisations.

The White House pointed to activist network Indivisible and the Open Society Foundations, founded by billionaire George Soros, as potential targets of scrutiny.

Although administration officials insist that their focus is preventing violence, critics see an extension of Mr Trump’s campaign of retribution against his political enemies and an erosion of free speech rights.

Any moves to weaken left-of-centre groups could also shift the political landscape ahead of next year’s mid-term elections, which will determine control of Congress and state legislatures across the US.

“The radical left has done tremendous damage to the country,” Mr Trump told reporters on Tuesday morning as he left for a state visit to Britain. “But we’re fixing it.”

He has sometimes made similar threats without taking any action. But now there is renewed interest, fuelled by anger over the killing of Mr Kirk, a far-right activist who was a prominent supporter of Mr Trump and a friend of many of his advisers.

Dozens of non-profit leaders, representing organisations including the Ford Foundation, the Omidyar Network and the MacArthur Foundation, published a joint letter saying: “We reject attempts to exploit political violence to mischaracterise our good work or restrict our fundamental freedoms.

“Attempts to silence speech, criminalise opposing viewpoints and misrepresent and limit charitable giving undermine our democracy and harm all Americans,” they wrote.

Indivisible’s leadership has said that “political violence is a cancer on democracy,” adding that their own organisation has “been threatened by rightwingers all year.”

US authorities said they believe the suspect in Mr Kirk’s assassination acted alone. He was charged him with murder on Tuesday.