"There is no need for this kind of talks," an unidentified spokesman told reporters at Beijing's airport, reading from a statement as the North Korean delegation was leaving the Chinese capital. "This round of talks was nothing more than empty talks."
"We no longer have interest, or expectations either, for this kind of talks," he added. "We are left with no option."
Also Saturday, North Korea's official KCNA news agency reported an unidentified North Korean Foreign Ministry spokesman as saying: "We have become much more sure that we have no other option but to increase our nuclear deterrent force for self-defense to protect our sovereignty."
Less than two hours earlier, Assistant Secretary of State James Kelly, who represented the United States in the talks, said all parties had gotten off to "a productive start."
The U.S. Embassy in Beijing and the South Korean government did not immediately comment on the North Korean delegation's remarks. The Chinese Foreign Ministry said the issue was "extremely complex and cannot be resolved with one or two discussions."
"The relevant parties reached quite a few common understandings but there were also quite a few differences. This is normal," the ministry said in a statement. "There is a long road that still needs to be walked and we hope all parties will continue to work hard toward progress."
The three-day, six-country talks in Beijing were the result of months of delicate political maneuvering. China, which is North Korea's last major ally, also played host to diplomats from Japan, South Korea and Russia.
Tensions have been growing since last October, when North Korea acknowledged to Kelly that it had restarted its nuclear weapons program.
The United States has insisted on "the complete, verifiable and irreversible elimination" of North Korea's nuclear weapons program before it can seriously consider improving relations with the North. But the impoverished Stalinist regime has refused to comply without security and economic aid guarantees.
All the governments represented at the Beijing talks had expressed varying degrees of opposition to the North's nuclear ambitions. China has said repeatedly that it wants a nuclear-free Korean Peninsula.
The delegates from the six countries said the main goal of the gathering was to establish an opening for future talks and address North Korea's security issues. No date or venue was established, but China Central Television reported that fresh meetings would take place within two months.
"We've had a nice visit to Beijing, a productive start," Kelly told reporters before leaving for the airport. "We've got a very long way to travel."
He added: "But a peaceful solution is something we're going to work on."
The brinkmanship and bluster that has characterized North Korea's diplomacy surfaced on the second day of the talks, when North Korea said it would prove to the world it possesses nuclear weapons by testing a nuclear device, according to a U.S. official who spoke on condition of anonymity.
In Washington, State Department press officer Jo-Anne Prokopowicz said Friday that the threats "are not a surprise."
"The U.S. will not respond to threats or give in to blackmail," she said. "These threats only serve to further isolate North Korea from the international community."
But North Korean Vice Foreign Minister Kim Yong Il also showed a willingness to compromise, suggesting that his country would abandon the nuclear weapons program if the United States agreed to its conditions.
"It is not our goal to have nuclear weapons," KCNA quoted Kim as saying.
The delegation spokesman at the airport, however, reverted back to North Korea's original rhetoric.
"This is not just a difference in opinion but a difference in fundamental policies," the spokesman said. "We have come to conclude that the United States has no intention for a policy switchover and it plots to disarm our country through sinister schemes."
In Tokyo, Japan's Defense Agency unveiled plans to seek 142.3 billion yen (the equivalent of $1.21 billion American dollars) in funding for two U.S.-designed ballistic missile defense systems, spurred by concern over North Korea's long-range missiles.
Japan has been conducting joint research with the United States on theater missile defense since 1999 - a year after the test-launch of a North Korean Taepodong missile that flew over Japanese airspace. The incident showed that virtually all of Japan could be targeted by North Korean missiles.