The killing of the rightwing activist Charlie Kirk at a Utah college on Wednesday afternoon prompted outrage from Democrats and Republicans over the latest act of political violence in the United States, with Donald Trump lamenting the loss of a key ally.

“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,” the US president posted on his Truth Social platform.

The president ordered flags to be lowered to half mast to honor Kirk, who was prominent in Trump’s make America great again (Maga) movement.

Trump, who survived an assassination attempt while campaigning in July 2024, also blamed the violence on the “radical left [who] have compared wonderful Americans like Charlie to Nazis” in an evening video address. “This kind of rhetoric is directly responsible for the terrorism that we’re seeing in our country,” he said.

The identity and motives of the shooter, who was not in custody early Wednesday evening, are not yet known.

JD Vance called Kirk “a genuinely good guy and a young father” and tweeted prayers.

Secretary of state Marco Rubio said he was “heartbroken and outrages [sic] by the assassination of Charlie Kirk,” calling the 31-year-old “an incredible husband and father and a great American”.

Former vice-president Kamala Harris said she was “deeply disturbed” by the shooting of Kirk, who organized against her presidential campaign last year.

“Let me be clear: 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,” she wrote.

Congress’s top Republicans and Democrats joined in the condemning the attack, which occurred at Utah Valley University in Orem, south of Salt Lake City. “Political violence, which this attack seems to be, has no place in this country – none,” said John Thune, the Republican Senate majority leader.

“I’m deeply disturbed about the threat of violence that has entered our political life, and I pray that we will remember that every person, no matter how vehement our disagreement with them, is a human being and a fellow American deserving of respect and protection.”

Hakeem Jeffries, the Democratic House minority leader, echoed the sentiment, saying: “Political violence of any kind and against any individual is unacceptable and completely incompatible with American values.” And Ken Martin, chair of the Democratic National Committee, said “in all likelihood, [Kirk] was murdered for expressing his beliefs,” adding: “We must work harder to bring this country together, not divide it.”

Gabby Giffords, whose time as a congresswoman was cut short when she was grievously injured in a 2011 mass shooting, said: “Democratic societies will always have political disagreements, but we must never allow America to become a country that confronts those disagreements with violence.”

The House oversight committee took a break from considering more than a dozen bills to change laws in Washington DC as part of Trump’s militarized crackdown on crime in the district to hold a moment of silence in Kirk’s honor.

Barack Obama condemned political violence as “despicable” and said it had “no place in our democracy”.

“We don’t yet know what motivated the person who shot and killed Charlie Kirk, but this kind of despicable violence has no place in our democracy,” he wrote. “Michelle and I will be praying for Charlie’s family tonight, especially his wife Erika and their two young children.”

Democrats seen as potential presidential contenders in 2028 also denounced the violence.

“The attack on Charlie Kirk is disgusting, vile, and reprehensible. In the United States of America, we must reject political violence in EVERY form,” said Gavin Newsom, the California governor.

Wes Moore, the Maryland governor, wrote on X: “Political violence is never acceptable. Ever.”

New Jersey senator Cory Booker, a Democrat, said the attack “must be condemned by all”.

Katie Hobbs, the Democratic governor of Arizona where Kirk headquartered his rightwing non-profit, Turning Point USA, said she was “deeply saddened” by his death.

“This tragedy is not about who Charlie Kirk supported politically. It is about the devastating loss of a father, a neighbor and an Arizonan,” Hobbs said.

“We must stand together in rejecting violence, lowering the temperature of our politics and recommitting ourselves to the values of civility, respect, and community that American democracy requires.”

The state’s Democratic US senator Ruben Gallego called Kirk’s death “beyond terrible”, adding: “Violence is never the answer.”

Some conservatives echoed Trump and were quick to blame liberals for the shooting while the search for the shooter was still under way.

“The Left is the party of murder,” said Elon Musk, the Tesla CEO who threw the federal government into turmoil earlier this year as chair of Trump’s department of government efficiency initiative.

Christopher Rufo, a conservative operative who led rightwing attacks against critical race theory in recent years, wrote on X: “The last time the radical Left orchestrated a wave of violence and terror, J Edgar Hoover shut it all down within a few years. It is time, within the confines of the law, to infiltrate, disrupt, arrest, and incarcerate all of those who are responsible for this chaos.”

Chaya Raichik, operator of the rightwing Libs of TikTok account, wrote to her 4.3 million followers on X: “THIS IS WAR”.

Hasan Piker, the progressive commentator who was scheduled to debate Kirk at an event hosted by Dartmouth College’s political union later this month, watched the video of his opponent being shot while streaming on Twitch.

“This is insane. I never thought I would see something like this. But I guess if there’s one country where something like this could happen, it’s this one,” he said.

Sam Levin contributed reporting