US President Donald Trump has issued a call for a primary challenger against hardline conservative Representative Lauren Boebert after she campaigned for maverick Representative Thomas Massie in his Kentucky district.

Boebert, a Colorado congresswoman and until now a staunch Trump ally, faced a public rebuke from the President for standing by the Kentucky Republican.

"Boebert is campaigning for the Worst 'Republican' Congressman in the History of our Country, Thomas Massie, of the Great Commonwealth of Kentucky, and anybody who can be that dumb deserves a good Primary fight!" Trump wrote on social media.

He later added: "Is anyone interested in running against Weak-Minded Lauren Boebert in Colorado's Fourth Congressional District? Just let me know, or announce your Candidacy, and I will be there for you!"

Boebert responded with a post on X, stating she was "not mad or offended" by the President's comments.

"I knew the risks when I agreed to stand by my friend Thomas Massie. I was, and will be, America First, America Always, and MAGA," she wrote.

Trump has vowed to unseat Massie, who has defied the President in Congress over major legislation and the Iran war.

Massie also led a drive to release government files on the late disgraced sex offender Jeffrey Epstein.

The President's quest to unseat the congressman poses a test for his hold on the Republican Party.

The social media posts have come just hours after Boebert appeared for Massie, who faces Trump-endorsed challenger Ed Gallrein, a retired Navy SEAL, in Tuesday's Republican primary.