Ahead of a potential summit between Donald Trump and Kim Jong-un, their negotiators are trying to hash out details over an array of hitherto intractable issues, including denuclearization methods, timelines and security assurances for the isolated regime.
A flurry of working-level talks over the past few days have raised cautious optimism for a denuclearization deal, which would also significantly affect the leaders' political fortunes at home and their images abroad.
But it still remains uncertain whether the longtime foes will find common ground ahead of their historic summit likely to occur on June 12 in Singapore.
"Trump and Kim may strive to craft a win-win solution that would not compromise the international nuclear non-proliferation regime, and would satisfy them in light of their domestic political gains," Nam Chang-hee, a diplomacy professor at Inha University, told Yonhap News Agency.
"But to achieve the complete denuclearization (of the North) may take more time than expected," he added, pointing to a complicated disarmament process that may call for the dismantlement of Pyongyang's "past, present and future" nuclear arms.
Facing midterm elections in November and a presidential vote in 2020, Trump has been pushing for a swift and stringent disarmament of the North, which would apparently also involve the destruction of chemical and biological weapons and ballistic missiles.
As part of its efforts for a "complete, verifiable and irreversible" denuclearization, Washington has demanded Pyongyang ship an estimated up to 20 nuclear warheads overseas at an early date, Japan's Kyodo News reported on Monday.
Estimates vary as to the size of the North's nuclear stockpile.
According to Seoul's 2016 defense white paper, the North possesses 50 kilograms of plutonium -- an amount that could yield up to 10 nuclear warheads. Some estimates put the number at up to 60 kg.
"Washington's concept of complete denuclearization targets all of the North's programs related to its fissile materials, nuclear production, enrichment, storage and research facilities," a government researcher said, declining to be named.
"So the key issue in the bilateral negotiations will be to what extent the North would accede to the U.S. demand," he added.
During the two inter-Korean summits on April 27 and May 26, the North Korean ruler affirmed his intention for the "complete denuclearization" of the peninsula. But he is unlikely to relinquish his nuclear arsenal before Washington offers sustainable security guarantees, observers said.
Pyongyang, with an ill-equipped conventional military force, has long regarded its nuclear arsenal as principal means to counter "U.S. hostility" and ensure its regime's security.
One of the North's key concerns is the likelihood of any deal being reversed after a change of government in Washington.
"The North's distrust towards the U.S. might have been amplified, as it has witnessed Trump scrapping many deals that the preceding Barack Obama government had clinched, such as the climate change accord, the Trans-Pacific Partnership and the Iranian nuclear deal," Kim Tae-hyun, a diplomacy professor at Chung Ang University, said.
To address the North's security concerns, U.S. Secretary of State Mike Pompeo has said that Washington would seek security assurances for Pyongyang "in the same way we are demanding a permanent, irreversible denuclearization."
The secretary has also hinted that the U.S. government would seek to gain congressional approval for any deal with the North to make it permanent.
The timetable for denuclearization is expected to be a major sticking point, as Trump eyes a fast process to apparently help create a conducive political environment ahead of the midterm elections, while Kim seeks security guarantees and sanctions relief in return for steps toward denuclearization.
"Trump will attempt to fix a specific date for the North's denuclearization and demand initial disarmament steps to show that his negotiations with the North are different from the past ill-fated ones," Park Won-gon, a security expert at Handong Global University, said.
When it comes to the timeline, Kim is also in a hurry given that he has been pushing to make the North an "economically strong" country by 2020 under his ambitious five-year development plan.
The timeline aside, Trump may seek a deal that would look better than the Iranian nuclear accord from which the U.S. has recently withdrawn. Anything less than the Iranian deal could trigger political censure and cast doubts over his much-vaunted deal-making prowess.
Another key point of bilateral negotiations is verification of the North's denuclearization process, a tough issue that impeded past negotiations.
"(Former U.S. President) Ronald Reagan once said, 'Trust but verify,'" Michael Raska, assistant professor at the S. Rajaratnam School of International Studies of Nanyang Technological University in Singapore.
"In other words, while trust is a necessary condition for a diplomatic engagement, it's the verification that matters," he added.
Despite its professed will to denuclearize, uncertainty still lingers over whether Pyongyang would accept the intrusive verification procedures, such as allowing international inspectors to access all of its nuclear facilities.
But guarded optimism has emerged that Pyongyang could take a more cooperative stance after Trump nixed the planned summit with Kim last Thursday, citing "open hostility" from the North. Following the North's conciliatory gesture and the South's mediation, Trump indicated that the summit could go ahead as initially planned.
Washington and Pyongyang appear to still be struggling to bridge their many differences, but what the two leaders appear to agree on is the need to create the optics of them taking historic steps towards mutual trust, denuclearization and a lasting peace on the peninsula, analysts said.
In the late 1980s during the Cold War, the then-Soviet Union staged a public event to destroy SS-20 medium-range nuclear missiles -- a centerpiece of its military threat to American allies in Europe -- in a major symbolic gesture for peace and confidence building.
Pyongyang could publicly dismantle -- or ship overseas -- its intercontinental ballistic missiles (ICBMs), which pose a direct security threat to the U.S. mainland, observers said.
They added that in the past, Washington's top priority appeared to be preventing the voluntary or involuntary proliferation of nukes from a failed or failing regime in Pyongyang. But the North's possession of ICBM technology has apparently prompted the U.S. to push for its complete denuclearization.