US President Donald Trump and North Korean leader Kim Jong Un pledged on Tuesday to work toward complete denuclearisation of the Korean peninsula while Washington committed to provide security guarantees for its old enemy, reported Reuters.

The two leaders had a one-on-one meeting, with translators only, followed by an expanded meeting including their top aides and a working lunch at Capella Singapore hotel in Sentosa Island after months of diplomatic twists and turns.

"We're signing a very comprehensive document, and we've had a really great time together, a great relationship," Trump said while signing the document along with Kim in the presence of media at the end of the summit - the first between a sitting US president and North Korea's top leader.

Trump committed to provide unspecified “security guarantees” to Kim as the two nations agreed to establish new relations “in accordance with the desire of the peoples of the two countries for peace and prosperity.”

The US President said he expected the denuclearisation process to start “very, very quickly”. US Secretary of State Mike Pompeo and North Korean officials would hold follow-up negotiations “at the earliest possible date”, the statement said.

But the agreement, which appeared to echo the April 27 Panmunjom Declaration signed between Kim and South Korean President Moon Jae-in, offered no specifics about how the two sides would reach these goals, while also leaving “complete denuclearization” undefined.

At a signing ceremony, Trump said the two sides had developed a “special bond,” while Kim, sitting beside him, called the summit a “historic encounter where we decided to leave the past behind.”

“The world will see a major change,” Kim said through a translator.

"I think our whole relationship with North Korea and the Korean peninsula is going to be a very different situation than it has in the past," Trump said at the conclusion of the landmark summit, which culminated in formal signing ceremony.

What precisely was agreed upon during the nearly five-hour summit was not initially clear as the two leaders sat next to each other and autographed documents in leather binders, reported CNN.

Asked by reporters asked if the agreement was the starting point for a process that would begin the denuclearization of Korean Peninsula, Trump said that such steps would happen “very, very quickly.”

Majority of the world leaders have welcomed the move with China asking for the immediate lifting of sanction against North Korea.

China "welcomes and supports" talks between North Korea and the US to reach consensus on denuclearisation and establish a peace mechanism, said Foreign ministry spokesman Geng Shuang.

"The UN Security Council could consider suspending or lifting sanctions against North Korea if Pyongyang is in compliance with UN resolutions and making progress in diplomatic negotiations," he added.

Geng later told reporters in Beijing: "Sanctions are not an end. We believe the Security Council should make efforts to support the diplomat efforts at the present time."

Japanese Prime Minister Shinzo Abe welcomed Kim's written commitment to complete denuclearisation.

"We see this as a step in a comprehensive resolution," Abe said in Tokyo.

Abe added that he "would like to thank the president (Trump) for raising the abduction issue," referring to Japan's demand that Pyongyang release any remaining Japanese people it abducted to train its spies.

South Korean President Moon Jae-in vowed to write "new history" with North Korea, praising Kim's decision to hold the summit with the US.

"Leaving dark days of war and conflict behind, we will write a new chapter of peace and co-operation," Moon said in a statement released by his office. "We will be there together with North Korea along the way," he added.

Moon's comments came after earlier caution from the presidential office, saying it was seeking clarity after Trump pledged to stop joint military exercises with Seoul.

"At this point, we need to find out the precise meaning or intentions of President Trump's remarks," a Blue House spokesman said.

Russia too hailed the deal between Trump and Kim, but sarcasticaly said "the devil is in the detail."

Deputy Foreign Minister Sergei Ryabkov told TASS news agency that Russia was ready to assist in implementing the deal - to work towards complete denuclearisation of the Korean peninsula - and hopes settling the nuclear crisis will unblock normal economic co-operation.

Russian Foreign Minister Sergei Lavrov also approved of the meeting, Interfax reported.

"The mere fact of the meeting between the leaders of the United States and North Korea is positive ... We are following the comments that both sides are making but we have not seen the document yet, we'll see," Lavrov said.

However, the Iranian government warned the US president could nullify any nuclear deal.

The semi-official Fars news agency quoted government spokesman Mohammad Bagher Nobakht as saying: "We are facing a man who revokes his signature while abroad."

"We don't know what type of person the North Korean leader is negotiating with. It is not clear that he would not cancel the agreement before returning back home."

The US pulled out of the landmark 2015 nuclear deal with Iran in May

The European Union, meanwhile, has welcomed the historic deal said the summit demonstrated that diplomacy paved the way forward to peace in the region.

"The ultimate goal, shared by the entire international community and as expressed by the United Nations Security Council, remains the complete, verifiable and irreversible denuclearisation of the Korean Peninsula," Federica Mogherini, the EU's high representative for foreign affairs, said in a statement.

"The joint statement signed by the US and DPRK (Democratic People's Republic of Korea) leaders today gives a clear signal that this goal can be achieved," she added.

UK hailed it as an important step towards the stability of a region vital to global economic growth.

"We welcome that President Trump and Kim Jong Un have held a constructive summit. There is much work to be done and we hope that Kim continues to negotiate in good faith towards complete verifiable and irreversible denuclearisation," Foreign Minister Boris Johnson said in a statement.