U.S. President Donald Trump abruptly cut short his summit with North Korean leader Kim Jong Un on Thursday without agreement, after failing to bridge the gap between his insistence on full-fledged denuclearization measures and Kim's demand for full sanctions relief.

"Basically they wanted the sanctions lifted in their entirety," Trump said at a news conference after the two-day talks in Vietnam's capital Hanoi by a few hours. "But we couldn't do that."

Kim pledged to "totally" dismantle his country's main Yongbyon nuclear complex, according to Trump. But the lifting of the sanctions would also require Pyongyang to scrap other nuclear facilities and programs, including undeclared ones, he said.

The second Trump-Kim meeting appeared to have been proceeding amicably, at least until Thursday morning, when Kim expressed readiness to give up nuclear weapons and ballistic missiles.

"If I'm not willing to do that, I won't be here right now," Kim said, speaking through an interpreter. He added the two leaders were discussing concrete steps for denuclearization of his country.

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[VNA/Kyodo]

Trump and Kim even welcomed the idea of the United States setting up a liaison office in Pyongyang as part of confidence-building measures.

They were believed to have discussed the possibility of issuing a declaration ending the Korean War, a 1950-1953 conflict that was halted with an armistice. North Korea regards such declaration as a first step toward guaranteeing its security.

Trump apparently pushed for the verifiable dismantlement of Yongbyon and other weapons facilities in exchange for issuing an end-of-war declaration or partial sanctions relief so that inter-Korean economic projects can move forward.

Given Trump's apparent eagerness to claim a big foreign policy win in the run-up to his 2020 re-election bid and his desire for the Nobel Peace Prize, speculation had grown that the president may be tempted to focus on less challenging issues such as declaring an end to decades-long enmity with North Korea.

The two leaders called off a planned working lunch and joint agreement signing ceremony, an event that had been meant to be a climax for the summit.

"We just felt it wasn't appropriate to sign an agreement today," Trump said. On Wednesday, he called for a "right deal" with Kim.

Speaking alongside Trump at the press conference Thursday, U.S. Secretary of State Mike Pompeo -- who attended the Hanoi summit -- said the president asked Kim to do more, but "he was unprepared to do that."

Analysts hailed Trump for walking away from what some called a "flashy but poorly crafted deal" with Kim.

"Trump correctly emphasized principles and longtime allies over a premature peace declaration and his newfound relationship with Kim Jong Un," said Bruce Klingner, the senior research fellow for Northeast Asia at the Heritage Foundation, a Washington think tank.

"While details remain unclear, it appeared North Korea offered only its Yongbyon nuclear facility in return for removal of all sanctions. While tempting, a bad deal is indeed worse than no deal," Klingner said.

U.S. officials and experts have expressed hope that the two sides will show tangible progress beyond the vague commitments agreed to by Trump and Kim at their last meeting, the first-ever U.S.-North Korea summit that was held in Singapore last June.

Kim had promised then to work toward "complete" denuclearization of the Korean Peninsula, while Trump committed to providing security guarantees to Pyongyang.

Despite the two leaders reaching no agreement at the Hanoi summit, Trump denied the event ended without progress, citing Kim's promise to continue to suspend nuclear and missile testing.

He quoted Kim as saying he will not conduct testing of "rockets or missiles or anything having to do with nuclear."

"I trust him and I take him at his word," the U.S. leader said. "I hope that's true."

Asked if he agreed with Kim on a third summit, Trump said, "No we haven't...we'll see if it happens."