U.S. President Donald Trump said Thursday he will meet for the first time with North Korean leader Kim Jong Un on June 12 in Singapore in a bid to achieve the denuclearization of the Korean Peninsula.

The summit, the first encounter between a sitting U.S. president and a North Korean leader in the absence of diplomatic relations, comes after Kim and South Korean President Moon Jae In pledged last month to work for the "complete denuclearization" of the peninsula.

In the upcoming meeting, analysts will observe whether Trump and Kim agree on concrete measures with a time frame to rid North Korea of nuclear weapons and all ballistic missiles -- not only intercontinental ballistic missiles that can reach the United States but shorter-range ones capable of hitting South Korea and Japan.

"We're going to set the table. We're going to make a great deal for the world, for North Korea, for South Korea, for Japan, for China," Trump said at a rally in Indiana.

Earlier Thursday, he tweeted, "The highly anticipated meeting between Kim Jong Un and myself will take place in Singapore on June 12th. We will both try to make it a very special moment for World Peace!"

The announcement came hours after three U.S. citizens detained in North Korea returned home, a diplomatic outcome that cleared a major hurdle for the unprecedented meeting.

Asked by reporters if the return of the Americans is his proudest achievement, Trump said, "My proudest achievement will be -- this is part of it -- but will be when we denuclearize that entire peninsula."

(Trump applauds three Americans released from detention in North Korea)

In Singapore, Trump is expected to push Kim to take concrete action toward a complete, verifiable and irreversible denuclearization and dismantle all missiles and related facilities.

Along with the nuclear and missile issue, Trump has promised to press Kim to resolve the North's abduction of Japanese nationals in the 1970s and 1980s, an issue Japanese Prime Minister Shinzo Abe sees as a top priority for his government.

During April 27 talks with Moon at the truce village of Panmunjeom in the Demilitarized Zone between North and South Korea, Kim said he would abandon nuclear weapons if the United States agreed to formally end the 1950-1953 Korean War and promised not to commit aggression against the country.

Kim said Pyongyang will dismantle its only known underground nuclear test site in May, and that the North is prepared to have talks with Japan, according to South Korea's presidential Blue House.

Kim did not refer to the closure or abandonment of nuclear facilities other than the Punggye-ri site, where North Korea has carried out all of its six nuclear tests to date, starting in 2006 and continuing until the most recent and powerful one in September of last year.

(Kim Jong Un (L) and  Moon Jae In)

[Korea Summit Press Pool]

On Thursday, Trump expressed optimism about his engagement with Kim. Asked why Kim freed the detainees now, Trump said, "I really think he wants to do something and bring that country into the real world."

"I think this will be a very big success," he said, without elaborating.

But the U.S. leader has emphasized that Washington will maintain maximum pressure and sanctions on Pyongyang in coordination with the international community until the North denuclearizes.

In reference to broken promises by North Korea during nuclear negotiations in the past, Trump said recently he will not be cheated by Pyongyang.

He criticized previous U.S. administrations for giving North Korea too many concessions despite the country not abandoning its nuclear weapon ambitions.

Speaking to reporters on April 30, Trump warned to Kim, "If it's not a success, I will respectfully leave."

In reflection of Trump's such feelings, his national security adviser John Bolton said, "No one in the Trump administration has any illusions about the negotiations ahead."

In an op-ed piece carried in the Thursday edition of the Washington Post, Bolton underscored close coordination with Japan and South Korea over North Korea, and wrote that Chinese President Xi Jinping "will also play a critical role in any resolution to the North Korean nuclear threat."

(Punggye-ri Nuclear test site)

[DigitalGlobe/38 North via Getty/Kyodo]