US President Donald Trump has lashed out at Republican conservatives who helped torpedo healthcare legislation he backed, escalating a feud within his party that jeopardises the new administration's legislative agenda.

Trump threatened to try to defeat members of the Freedom Caucus - a bloc of conservative Republicans in the House of Representatives - in next year's congressional elections if they continued to defy him.

"The Freedom Caucus will hurt the entire Republican agenda if they don't get on the team, & fast. We must fight them, & Dems, in 2018!" Trump tweeted on Thursday morning.

House conservatives fought back.

"Most people don't take well to being bullied," said Representative Justin Amash, who compared Trump's approach to what a child does when they want to get their way.

Representative Raul Labrador, one of the founders of the Freedom Caucus, urged Trump in a tweet to "Remember who your real friends are. We're trying to help you succeed".

Trump's deteriorating relationship with Republican House conservatives could make it harder for him to pass his legislative agenda, which includes rewriting the US tax code, revisiting a healthcare overhaul and funding construction of a wall along the US-Mexican border.

Trump, a New York businessman who touted his skills as a deal maker in his bid for the White House, has repeatedly criticised Freedom Caucus members, blaming them for the defeat of legislation to repeal and replace former President Barack Obama's signature healthcare law.

Freedom Caucus members said the bill did not go far enough to dismantle the 2010 Affordable Care Act, popularly known as Obamacare.

Republican lawmakers still await key details on what Trump's priorities are in the monumental tax reform effort they want to launch.

Passing a budget for next year could also prove challenging.

Trump and the Freedom Caucus want to dramatically shrink domestic programs.

Moderate Republicans are aghast at proposals to cut popular programs that fund environmental cleanup and meals for senior citizens.

Most pressing is an April 28 deadline for approving new funding to keep the government running.