PALM BEACH, Florida (Reuters) - President Donald Trump said on Wednesday (April 18) that negotiations were under way for the release of three Americans held as prisoners in North Korea.

Speaking at a joint news conference with Japanese Prime Minister Shinzo Abe, Trump said: "We are likewise fighting very diligently to get the three American citizens back. I think there's a good chance of doing it. We're having very good dialogue."

A senior administration official said CIA Director Mike Pompeo, who visited Pyongyang secretly in recent weeks, brought up the case of the three prisoners in his talks with North Korean leader Kim Jong Un, and the United States was hopeful for their release.

Trump also said he hoped a planned meeting with Kim to discuss denuclearization would be successful but that he would walk out if it was not.

"If we don't think it's going to be successful ... we won't have it," Trump said, adding: "If the meeting, when I'm there is not fruitful, I will respectfully leave the meeting."

Trump, who was hosting Abe and his wife at his Mar-a-Lago resort in Florida, said a campaign of maximum pressure on North Korea would continue until Pyongyang agreed to give up its nuclear weapons.

"There's a bright path available to North Korea when it achieves denuclearization in a complete and verifiable and irreversible way. It will be a great day for them. It will be a great day for the world," he said.

Trump voiced hope on Wednesday (April 18) that North and South Korea, technically still at war, can pave the way to a lasting peace at a series of upcoming summits.

Trump made the comments amid a flurry of diplomatic activity that has fuelled hopes of a major breakthrough in the standoff with Pyongyang.

"We hope to see the day when the whole Korean peninsula can live together in safety, prosperity and peace," the US President told a joint press conference with visiting Japanese Prime Minister Shinzo Abe at his Mar-a-Lago retreat in Florida.