US right-wing activist and commentator Charlie Kirk has died following a shooting at an event at Utah Valley University.
Mr Kirk, 31, was addressing a large outdoor crowd at the college campus when the shooting happened.
He was transported to a hospital and underwent surgery, however in a post on his Truth Social platform, US President Donald Trump said that Mr Kirk had died.
"The Great, and even Legendary, Charlie Kirk, is dead. No one understood or had the Heart of the Youth in the United States of America better than Charlie," Mr Trump said.
"He was loved and admired by ALL, especially me, and now, he is no longer with us."
US authorities have detained a suspect in the fatal shooting, FBI Director Kash Patel has said.
"The subject for the horrific shooting today that took the life of Charlie Kirk is now in custody," Mr Patel said on X. "We will provide updates when able."
Meanwhile the Governor of Utah, Spencer Cox, described the death of Mr Kirk was a "political assassination".
"This is a dark day for our state. It's a tragic day for our nation. I want to be clear that this is a political assassination," Mr Cox told reporters.
Video clips of the incident circulating on social media showed Mr Kirk addressing the crowd at Utah Valley University when a loud crack that sounded like a gunshot rang out.
Mr Kirk moved his hand toward his neck as he fell off his chair, sending the attendees running.
The suspect likely fired from a rooftop, authorities said, adding that there were about 3,000 people gathered at the event.
Agents from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives were on the scene, Attorney General Pam Bondi said on X.
Watch: Witnesses describe Charlie Kirk shooting at campus event in Utah
Mr Kirk and the group he co-founded, Turning Point USA, the largest conservative youth organisation in the country, played a key role in driving young voter support for Mr Trump in November last year.
His events at college campuses nationwide typically draw large crowds.
After winning a second term at the White House, Mr Trump credited Mr Kirk for mobilising younger voters and voters of colour in support of his campaign during a rally in Phoenix in December.
"You had Turning Point's grassroots armies," Mr Trump said. "It's not my victory, it's your victory."
Mr Kirk had 5.2 million followers on X and hosted a podcast and radio programme, "The Charlie Kirk Show." He had also recently co-hosted "Fox & Friends" on Fox News.
He was part of an ecosystem of pro-Trump conservative influencers - including Jack Posobiec, Laura Loomer, Candace Owens and others - who have helped to amplify the president's agenda.
Mr Kirk frequently attacked mainstream media and engaged in culture war issues around race, gender and immigration, often in a provocative style.
Mr Trump said on social media that he had ordered all US flags flown at half-staff until Sunday in Mr Kirk's honour.
While the motive for the shooting is unknown, the United States is undergoing its most sustained period of political violence since the 1970s.
Reuters has documented more than 300 cases of politically motivated violent acts since supporters of Mr Trump attacked the US Capitol on 6 January 2021.
Who was Trump ally and conservative influencer Charlie Kirk?
In July 2024, Mr Trump was grazed by a gunman's bullet during a campaign event in Butler, Pennsylvania. A second assassination attempt two months later was foiled by federal agents.
In April, an arsonist broke into Pennsylvania Governor Josh Shapiro's residence and set it on fire while the family was inside.
Biden says violence 'must end now'
Both Republican and Democratic politicians have expressed dismay over the shooting.
"Eternal rest grant unto him, O Lord," Vice President JD Vance, who was close to Mr Kirk, wrote on X.
Former US president Joe Biden joined many other US politicians in condemning the shooting, and called for a halt to violence.
"There is no place in our country for this kind of violence. It must end now. Jill and I are praying for Charlie Kirk's family and loved ones," Mr Biden said on social media.
His former vice president Kamala Harris condemned the shooting, as US politicians from all sides expressed outrage at the attack.
"Political violence has no place in America. I condemn this act, and we all must work together to ensure this does not lead to more violence," Ms Harris said in a social media post.
"Political violence is NEVER acceptable," Hakeem Jeffries, the Democratic leader in the US House of Representatives, said on X. "My thoughts and prayers are with Charlie Kirk and his family."
Republican House Speaker Mike Johnson wrote on X, "Please join us in praying for our good friend, Charlie Kirk."
