US President Donald Trump on Sunday called slain right-wing activist Charlie Kirk "a giant of his generation" at a massive memorial event marked by strong Christian rhetoric and praise for the man many speakers referred to as a "martyr."

The 79-year-old Republican said Kirk was "above all a devoted husband, father, son, Christian and patriot," adding that he "was violently killed because he spoke for freedom and justice. For God and country. For reason and for common sense."

The service drew an extraordinary level of attention and security, with the top brass of Trump's administration joining tens of thousands in attendance, and some US media likening it to a state funeral.

Ahead of Trump's address, the crowd heard speeches from prominent cabinet members including Vice President JD Vance, Secretary of State Marco Rubio and Defense Secretary Pete Hegseth.

"You thought you could kill Charlie Kirk? You have made him immortal," top Trump advisor Stephen Miller said, vowing "to save this civilization, to save the West."

Among other speakers were right-wing media personality Tucker Carlson, Trump's Chief of Staff Susie Wiles and Director of National Intelligence Tulsi Gabbard.

The event was being hosted by Turning Point USA, the hugely influential youth political campaign group founded by Kirk that is now run by his widow, Erika Kirk, who also spoke at the memorial.

"That young man, I forgive him," Kirk said of her husband's alleged murderer, 22-year-old Tyler Robinson, a gesture that drew uproarious applause from the crowd.

State authorities have charged Robinson with murder and are pursuing the death penalty in the case against him.

At the event, Trump was seen sitting beside billionaire backer Elon Musk, whose acrimonious departure from the White House after his brief tenure overseeing the Department of Government Efficiency (DOGE) was not apparent as the two men chatted.

Thousands of people had lined up hours before the event began, hoping to get into the 63,000-seat American football stadium hosting the service and honor the young Republican star -- a close ally of the president whose voter outreach is credited with helping Trump get reelected last year.

"I look at him as a Christ martyr, definitely," Monica Mirelez, a 44-year-old Texan who drove 12 hours to get there, said of Kirk.

Jeremy Schlotman, a 21-year-old biology student, said Kirk gave him the courage to express his beliefs on campus.

"For example, I think that biological men shouldn't be in women's sports. But I was too afraid to talk about stuff like that out loud," Schlotman said as Christian bands played on stage and the stadium steadily filled up.

'Hatred'

Kirk, 31, was shot in the neck on September 10 while speaking at a Utah university as part of his popular public debate series. Authorities arrested a suspect after a 33-hour manhunt.

The killing has inflamed often acrimonious and sometimes violent political divisions in the United States.

Authorities say the suspected gunman cited the "hatred" he believed was stoked by Kirk -- who was a vitriolic critic of transgender people, Muslims and others.

Kirk used his millions of social media followers, the massive audience of his podcast and appearances at universities to bolster Trump with young voters and fight for a nationalist, Christian-centric political ideology.

Even before the alleged killer was identified or arrested, Trump called Kirk "a martyr for truth and freedom" and blamed the rhetoric of the "radical left."

Crackdown on liberal 'terrorism'

In response to the killing, the White House last week declared it would crack down on what it terms "domestic terrorism" by the political left. 

Trump said he would designate "Antifa" -- a shorthand term for "anti-fascist" used to describe diffuse far-left groups -- as "a major terrorist organization," a move he threatened in his first term.

On Sunday, Trump said his government would go after alleged "networks" responsible for left-wing violence.  

Prominent late-night talk show host Jimmy Kimmel was yanked off the air Wednesday, hours after the government threatened to cancel broadcasting licenses because of comments he made about Kirk's killing.

The moves have sparked alarm among Trump's critics who warn of possible steps to silence dissent of his divisive right-wing White House tenure, marked by a rolling back of social justice policies and an immigration crackdown that has seen widespread complaints of rights abuses.

by Romain Fonsegrives, with Asad Hashim in Washington