The US President, Donald Trump has made his feelings towards his opponents clear in no uncertain terms.

Trump spoke at the funeral of Charlie Kirk, the conservative activist who was gunned down at Utah Valley University.

Trump was the last speaker, after Kirk's widow Erika, and walked on stage as Lee Greewald sang his song, “God Bless the USA”.

The president called Kirk’s killer a “radicalised, cold-blooded monster”.

“He was violently k!lled because he spoke for freedom and justice, for God, country, for reason, and for common sense,” he said.

Trump said Kirk has become “immortal” and that he is a “martyr” for American freedom.

“Our greatest evangelist for American liberty became immortal,” he said. “He’s a martyr now for American freedom.”

Trump referred to liberals as “the radical left lunatics,” drawing some laughs from the crowd.

The president said he and Kirk were different in how they viewed their political enemies.

“He was a missionary with a noble spirit and a great, great purpose. He did not hate his opponents. He wanted the best for them,” Trump said. “That’s where I disagreed with Charlie. I hate my opponent, and I don’t want the best for them.”

The president apologised to Kirk’s widow for that difference.

“Erika, you can talk to me and the whole group, but maybe they can convince me that that’s not right, but I can’t stand my opponent,” he said.