US authorities investigating the killing of right-wing youth leader Charlie Kirk said there had been "rapid developments" Thursday as they released pictures of a man they were hunting.

Kirk, a 31-year-old superstar on the Republican right who Donald Trump lauded as a "giant of his generation," was shot while addressing a large crowd at Utah Valley University on Wednesday.

The killing -- described by the FBI as a "targeted event" -- shocked a nation already reeling from political tensions half a year into Trump's second term.

Authorities acknowledged the gunman remained at large after escaping into woodland.

"We're doing everything we can to find him, and we're not sure how far he has gone yet," FBI Special Agent Robert Bohls told a media briefing.

Authorities said the suspect was of u

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