The United States on Friday ended nuclear arms talks with North Korea with a message that the "path is open" to better relations if the reclusive North shows a firm commitment to disarmament efforts.

Both sides gave a cautiously optimistic assessment of two days of talks at the US mission to the United Nations in New York, though neither gave any indication of a breakthrough.

Diplomats and experts have warned that it will be a painstaking process to get North Korea, which staged atomic weapons tests in 2006 and 2009, back to talks with international powers on scrapping its arsenal.

"We reiterated that the path is open to North Korea towards the resumption of talks, improved relations with the United States, and greater regional stability if North Korea demonstrates through its actions that it supports the resumption of the six party process as a committed and constructive partner," US envoy Stephen Bosworth said after the talks.

North Korea's first vice foreign minister, Kim Kye-Gwan, also spoke briefly to reporters to thank them for covering the two days of talks.

He said "the talks were very constructive and businesslike" and that he would "remain in touch" with Bosworth and US diplomats. Just as no details of the negotiation positions were given, neither side said whether a new meeting was planned.

North Korea agreed in principle in 2005 with the United States, China, South Korea, Japan and Russia to scrap its atomic weapons program in return for economic aid and better relations.

But it staged a nuclear test in 2006, pulled out of the six nation talks in late 2008 and then exploded a second nuclear bomb in 2009.

Last year, an artillery attack on a South Korean island on the tense Korean frontier after the earlier sinking of South Korean warship added new hammer blows to hopes for long term peace.

The talks between Bosworth and Kim were the first top level contacts between the Cold War rivals since Bosworth, the US special representative on North Korea, went to Pyongyang in December 2009.

But China has convinced President Barack Obama's administration that it is imperative to draw North Korea back into the six-nation talks, diplomats said.

US Secretary of State Hillary Clinton invited North Korea to the talks after a meeting in Indonesia last week between envoys from North and South Korea. But she said no new incentives would be offered to North Korea.

"As we have said from the beginning of these discussions, they are designed to explore the willingness of North Korea to take concrete and irreversible steps toward denuclearization," Bosworth said.

"In that regard, these were constructive and businesslike discussions."

He stressed that before deciding the "next steps to resume the process," the US administration will "consult closely" with South Korea and other countries in the disarmament talks.

Diplomats and experts have stressed the high level of mistrust between North Korea and the rival South and its US ally, which has caused multiple false starts in attempts to coax North Korea out of its isolation.

"The absence of trust on both sides is at this point so significant that a kind of grand bargain (between the US and North Korea) is unlikely," said Charles Kupchan, a professor of international relations at Georgetown University in Washington.

Scott Snyder, a Korea specialist at the Council on Foreign Relations think tank, said the United States should consider demanding that North Korea no longer send Kim Kye-Gwan to talks.

Kim has been negotiating with a series of US envoys over the past two decades.

"His longevity in the job shows he has earned the backing of his leadership, but from a US perspective, the result of negotiations with Kim Kye-Gwan has been an abject failure," Snyder said in his Asia Unbound blog.

"As long as Pyongyang sends out Kim Kye-gwan as the regimes face to the United States, there is little reason to harbor expectations that current contacts will yield results different from the past.

"The United States should insist on a new man -- and new instructions -- from Pyongyang if the dialogue is to continue," Snyder said.