Washington: President Donald Trump urged evangelical leaders this week to get out the vote ahead of the upcoming midterm elections and warned of "violence" by opponents if they fail.

Trump made the dire warning at a White House dinner Monday evening attended by dozens of conservative Christian pastors, ministers and supporters of his administration.

Trump was stressing the stakes in November when he warned that, if Democrats win, they "will overturn everything that we've done and they'll do it quickly and violently," according to attendees and audio of his closed-door remarks obtained by media outlets, including The New York Times. He specifically mentioned self-described antifa, or anti-fascist groups, describing them as "violent people".

Asked Wednesday what he meant, Trump told reporters, "I just hope there won't be violence".

"If you look at what happens ... there's a lot of unnecessary violence all over the world, but also in this country. And I don't want to see it," Trump said.

At the dinner, Trump talked up his administration's efforts to bolster conservative Christian causes and urged those gathered to get their "people" to vote, warning the efforts could quickly be undone.

"I just ask you to go out and make sure all of your people vote," Trump said, according to the Times. "Because if they don't — it's Nov. 6 — if they don't vote we're going to have a miserable two years and we're going to have, frankly, a very hard period of time because then it just gets to be one election — you're one election away from losing everything you've got".

Ohio Pastor Darrell Scott, an early Trump supporter who attended the dinner, said he interpreted the comments differently than the media has portrayed them.

"It wasn't any kind of dire warning," Scott said, "... except for the things that we've been working on as a body of voters will be reversed and overturned".

"What he was saying," Scott continued, is that "there are some violent people ... but it wasn't that we've got to worry about murder on the streets and chaos and anarchy... just that the things we've worked for will be overturned".

Tony Perkins, the president of the Family Research Council and another attendee, said he, too, interpreted Trump's message as a warning not to be complacent.

While Trump did make a reference to antifa, Perkins told CNN, "I don't think anybody in the room suggested that there was going to be violence across the nation".

"I did not interpret him to say that the outcome of the election is going to lead (to) violence in the streets, and violence in the churches," he told CNN.