SEOUL, This week's nuclear talks between U.S. President Donald Trump and North Korean leader Kim Jong-un ended fruitlessly Thursday as they played hardball over Washington's sanctions relief and Pyongyang's denuclearization amid pressure from home, analysts said.

In a crucial test of their "top-down" approach to the decadesold nuclear quandary, the leaders began their two-day negotiations in Hanoi Wednesday with boasts of their "very special" relationship, but ended up without a deal.

During a press conference after his talks with the North Korean leader, Trump suggested that his push for more denuclearization steps by the North, Kim's demands for complete sanctions lifting and concerns about possible criticism of a bad deal led him to walk away from the summit.

But he left open the possibility of future negotiations.

"It was about the sanctions. Basically they wanted the sanctions lifted in their entirety and we couldn't do that. They were willing to denuclearize a large portion of the areas we wanted but we couldn't give up all of the sanctions for them," he said.

"So we continue to work and we will see. But we had to walk away from that particular suggestion," he added.

During the summit, the U.S. side appeared to have demanded the North give up more than Pyongyang's mainstay Yongbyon nuclear complex, contrary to expectations that the leaders might agree to the shutdown or freeze of its key facilities as an initial step toward what they agreed to in their first summit in Singapore in June -- the complete denuclearization of the Korean Peninsula.

"We had to have more than that because there are other things that you haven't talked about and you haven't written about," Trump said.

Asked if he wanted to include the North's uranium enrichment facilities, the president said, "Exactly ... I think they were surprised we knew."

U.S. Secretary of State Mike Pompeo cited "timing and sequencing issues" as another sticking point.

"There were also timing and sequencing issues associated with that as well, which we didn't quite get across the finish line," he said.

"But remember too (that) even that facility -- the Yongbyon facility -- and all of its scope, which is important for sure, still leaves missiles, still leaves warheads and weapons systems, so there (are) a lot of other elements we couldn't get to," he said.

The conflicting interpretations of what complete denuclearization might look like appeared to be another stumbling block.

"(Kim) has a certain vision and it is not exactly our vision," Trump said, noting that the North's vision is now "a lot closer" than it was a year ago.

Analysts said that the latest nuclear showdown laid bare the limits of the top-down approach under which the leaders of the two countries agree on broad negotiation guidelines with their working-level negotiators fining-tuning details later.

The past failed negotiations were based on bottom-up approaches where negotiators haggled over details, struck compromises and reached agreements whose implementation was derailed amid a lack of political will among their leaders.

"During their Singapore summit, they agreed on just the broad direction of denuclearization, but when their officials with expertise met at the table to discuss details, they clashed and made little headway," Park Won-gon, professor of international politics at Handong Global University, said.

For Trump, potential public criticism of a bad deal appeared to be on his mind.

"I could have signed an agreement today, and then you people would have said what a terrible deal. You have to be prepared to walk," he said.

Trump has faced a series of challenges at home, including a probe into Russia's alleged link to his 2016 presidential campaign. Thus, he was expected to produce a deal that he could tout as a foreign policy coup.

Source: Yonhap news Agency