At a security forum in Seoul hosted by Yonhap News Agency and the Asia-Pacific Research Center (APARC) of Stanford University, they agreed that such a meek diplomacy has emboldened North Korea to improve its nuclear arsenal amid signs that a third nuclear test by the North is coming.
"When I consider where we are with North Korea today, compared with 13 years ago, I am compelled to conclude that diplomacy with North Korea in the past 13 years may well go down as the greatest diplomatic failure in our history," former U.S. defense chief William Perry told the forum.
Perry, who served as defense secretary under President Bill Clinton, said diplomacy with North Korea has allowed Pyongyang to "build a small nuclear arsenal, conduct two nuclear tests and prepare for another nuclear test."
"They have built at least two uranium enrichment facilities, probably using one of these to build highly enriched uranium to increase their nuclear arsenal," Perry said.
"One lesson we must learn from that is we should not continue the same losing diplomatic strategy," Perry said.
Tensions are high on the Korean Peninsula after North Korea threatened to conduct a third nuclear test in retaliation to a U.N. Security Council resolution that widened sanctions against Pyongyang for its December rocket launch.
Officials in Seoul have said North Korea has completed all preparations and could detonate a nuclear device at any time.
Siegfried Hecker, a nuclear scientist at Stanford University who was shown North Korea's modern uranium enrichment facility during a visit to the country in late 2010, called for South Korea and the U.S. to lay out a new policy aimed at limiting the North's nuclear threat before the North's nuclear ambitions become "an increasingly menacing and permanent fixture."
Hecker estimated that the North's nuclear threat is "still in its infancy."
"American and South Korean policies since 2002 designed to denuclearize North Korea have failed to halt the North's relentless march to enhance its nuclear programs -- from nuclear reactors, to uranium enrichment, to nuclear tests and its long-range missile capabilities," Hecker said.
"Yet, in spite of the North's threatening rhetoric, the nuclear threat is still in its infancy -- the worst is yet to come, unless the new administrations formulate policies that focus on limiting the threat," he said.
Numerous analysts have raised doubts over Washington's so-called "strategic patience" approach toward North Korea, a policy of shunning direct talks with the North until it agrees to abide by past nuclear commitments.
"North Korea has now categorically stated its nuclear weapons are not negotiable," Hecker said. "South Korean and American actions must focus on those weapons being a temporary hedge rather than an increasingly menacing and permanent fixture."
The six-nation talks, involving the two Koreas, the U.S., China, Russia and Japan, have been dormant since April 2009, when the North quit the negotiating table and conducted its second nuclear test a month later.
Pyongyang claims the uranium enrichment program is for peaceful energy development, but outside experts believe it will give the country a new source of fission material to make atomic bombs, in addition to its widely known plutonium-based nuclear weapons program.
Hecker said North Korea will likely conduct its third nuclear test with a highly enriched uranium (HEU) explosion because there is "no plutonium in the pipeline."
"The North's Yongbyon nuclear facility has a potential for 2 tons of low-enriched uranium fuel per year or 40 kilograms of HEU per year," Hecker said.
If North Korea follows through on its threats of a nuclear test with HEU, it will "potentially greatly expand size of their nuclear arsenal because we don't know when and where they enrich uranium because it is so easy to hide."
Hecker said the North's "uranium enrichment appears to have all requisite technologies."
The one-day forum, titled "Yonhap-Stanford APARC International Symposium," brought together a number of former and current government officials from the allies under the theme of "Northeast Asia under New Leadership." The conference takes place three weeks before President-elect Park Geun-hye is sworn into office amid near-simultaneous leadership changes in China and Japan.
"North Korea under the leadership of Kim Jong-un, who has been in power for the last year, launched a long-range missile in late 2012. In response to United Nations sanctions for the launch, the regime declared it would halt its denuclearization and implied the possibility of a nuclear test," said Park Jung-chan, the president and CEO of Yonhap News Agency, in his welcoming remarks.
Park said the forum is "a great opportunity to take a look at the current situations in Northeast Asia and the Korean Peninsula."
Tensions are high on the Korean Peninsula after North Korea threatened to conduct a third nuclear test in retaliation for a U.N. Security Council resolution that widened sanctions against Pyongyang for its December rocket launch.
In addition to North Korea's nuclear standoff, the conference aims to discuss bilateral issues between South Korea and the U.S., as this year marks the 60th anniversary of signing a mutual defense treaty between the two countries. The conference will also touch on Sino-U.S. relations under the leadership of Beijing's president-in-waiting Xi Jinping, organizers said.
During the forum, U.S. Ambassador to South Korea Sung Kim called on North Korea to avoid any "provocative" moves.
"We continue to call on the DPRK (North Korea) to avoid any provocative behavior, become a responsible neighbor, and return to an authentic and credible diplomatic process toward our shared goal of denuclearization," Kim said.
"The process will not happen overnight. It will not be easy," Kim said. "But we will continue to press forward, in cooperation with our friends and allies in the region, to help build a Northeast Asia full of peace and prosperity."