U.S. President Donald Trump says that he won't rule out direct talks with North Korean leader Kim Jong-un.

Trump made the comment on Saturday during a dinner with journalists in Washington. 

In a joke-filled speech, the president said that North Korea called up a couple of days ago and said it would like to talk to which he responded 'So would we, but you have to denuclearize.'

It was unclear if Trump was joking or he meant that North Korea contacted the U.S. through a certain channel to explore dialogue possibilities, or if he was referring to a senior North Korean official's recent comment hinting at the North's openness to dialogue with the U.S. 

Last week, Trump said that Washington will hold talks with North Korea only under the right conditions.

Regarding South Korea's dispatch of special envoys to North Korea, the U.S. State Department said Sunday that the U.S. and South Korea will work together through the maximum pressure campaign to ensure progress in inter-Korean relations is accompanied by advances towards denuclearization.

It stressed that the denuclearization of the Korean Peninsula is non-negotiable.