US President Donald Trump says his planned meeting with North Korean leader Kim Jong-un could fizzle — or it could result in “the greatest deal for the world” to ease nuclear tensions in the region.

Mr Trump told a campaign rally for a Republican congressional candidate in western Pennsylvania that he believed North Korea wanted to make peace, saying “I think it’s time.”

“Who knows what’s going to happen?” said Mr Trump. “I may leave fast or we may sit down and make the greatest deal for the world.”

A time and venue for the historic first meeting between the countries’ two leaders has not been announced but it is supposed to take place by the end of May.

Mr Trump made the decision to meet with Mr Kim last week after the North Korean leader’s invitation was relayed by a South Korean delegation who visited the White House.

The move abruptly reversed decades of US policy aimed at preventing North Korea from developing nuclear weapons and ballistic missiles.

Prior to the rally, Mr Trump attempted to rally international support for the summit, saying North Korea had agreed to not conduct another missile test until after proposed meetings had taken place.

It was not immediately clear which meetings Mr Trump was referring to, or their timing.

Under fire for agreeing to talks with North Korea, the White House responded by warning that no summit would occur unless Pyongyang took “concrete actions” over its nuclear program.

Mr Trump also took to Twitter to characterise the leaders of China and Japan as supportive of the potential dialogue, but did little to clear up confusion over the preconditions and timing of any talks.

Mr Kim and Mr Trump prompted jitters around the world last year as they exchanged insults over North Korea’s attempts to develop a nuclear weapon capable of hitting the United States.

Mr Trump’s sudden decision to meet Mr Kim stunned even people in his own administration.

Some US officials and experts worry North Korea could buy time to build up and refine its nuclear arsenal if it drags out talks with Washington.