WASHINGTON -- North Korea's recent threats against South Korea appear aimed at testing the South Korea-US alliance and opening up more gaps between the allies, a former senior US official said Monday.

North Korea has ratcheted up tensions on the Korean Peninsula with a series of threats to cut off all inter-Korean communication lines and even take military action over activists' flying of anti-Pyongyang leaflets into the North.

"I think, to some extent, what we've seen from North Korea in the last couple of weeks, which appears to be very much directed at the ROK and directed at the Moon (Jae-in) administration, is really directed in an effort to see how far the US and the ROK are in terms of how far apart are they, and I think it's kind of a testing of the alliance," Christopher Hill, former assistant secretary of state for East Asian and Pacific affairs, said during a virtual seminar hosted by the International Crisis Group, referring to South Korea by the acronym for its official name, the Republic of Korea.

"And so far we're doing very poorly, because of President Trump's obsession with this issue of host nation support for our military," he added, referring to US President Donald Trump's demands for a significant increase in Seoul's contributions to the upkeep of 28,500 American troops stationed in South Korea.

Hill, who also previously served as chief US envoy to the six-party nuclear talks with North Korea, expressed skepticism that North Korea will go ahead with its threat of military action against South Korea.

"I really do believe that what they're doing is more political in trying to humiliate the South Korean government, and they're trying to sort of open up more gaps between the ROK and the US," he said.

A North Korean provocation at this time would not only hurt the North's apparent wish to see Trump reelected but also damage its ties with China, Hill said.

Pyongyang's anger at Seoul comes amid no progress in denuclearization talks between the US and the North. Despite three meetings between Trump and North Korean leader Kim Jong-un, the two sides have failed to agree on the scope of North Korea's denuclearization and US sanctions relief, as well as the sequencing of their steps.

Robert Gallucci, a former chief US negotiator who produced the Agreed Framework with North Korea in 1994, had advice to give to a potential new administration under former vice president and Democratic candidate Joe Biden.

"I would like him to start in his reaction to the Korea case with the normal -- I don't want to say platitudes -- but necessary comments about how important the issue is, but make clear first that his administration will be committed as past American administrations have been to the denuclearization of North Korea," Gallucci said during the same seminar.

At the same time, he said, a Biden administration must require the North Koreans to address its human rights situation before normalizing bilateral ties.

Gallucci also said he favors a step-by-step and action-for-action approach, given the decades of mistrust between the US and North Korea.

"I don't know whether we need a specific roadmap, but we need some substance upfront with respect to both points, both on the normalization side and on the side of denuclearization," he said.

"So, if we were clear about that and we gave over the obligations to execute this to working-level negotiators, I think that would be the right course -- not excluding summitry, but not leaning to summitry," Gallucci said, adding that another Trump-Kim summit before the November presidential election would be a "bad idea." (Yonhap)