Upcoming US-North Korean talks will ease high tensions on the Korean peninsula but are unlikely to bring a quick breakthrough in years-long efforts to shut down the North's nuclear programme, analysts say.

US Secretary of State Hillary Clinton announced Sunday that the North's vice foreign minister Kim Kye-Gwan would visit New York this week for "exploratory talks" on possible resumption of long-stalled six-nation nuclear negotiations.

The invitation was announced after nuclear envoys from North and South Korea held talks in Indonesia on Friday, on the sidelines of an Asian security forum.

Those talks were followed by a brief but apparently cordial meeting the next day between the foreign ministers from the two sides.

The surprise encounters follow more than a year of cross-border acrimony, including repeated threats by the North's army of "merciless" retaliation for perceived insults by the South's forces.

Those tensions were complicating efforts to restart the six-party forum -- grouping the two Koreas, China, the United States, Russia and Japan -- which was last held in December 2008.

"North Korea realised that the only way to have dialogue with the US was to make nice to South Korea," said Peter Beck, a fellow with the US Council on Foreign Relations. "It's a modest breakthrough."

But Beck was "very sceptical" that the North -- despite US demands -- was willing to move beyond where the six-party talks left off, and said he was doubtful the forum would resume this year.

Washington does "not intend to reward the North just for returning to the table," Clinton said Sunday.

"We will not give them anything new for actions they have already agreed to take," she said. And we have no appetite for pursuing protracted negotiations that will only lead us right back to where we have already been."

Under a 2005 deal, the North agreed to scrap its nuclear weapons in exchange for major diplomatic and security concessions along with aid.

The deal foundered amid mutual accusations of bad faith, and the North staged two nuclear weapons tests. Last November it unveiled a uranium enrichment programme, a potential second route to a bomb.

"The Obama administration has set the bar too high to make progress," Beck told AFP. "Talking is better than not talking, but sooner or later, it has to realise that the best thing it can achieve is to freeze the North's programme."

The North's rulers for their part "have decided for the time being that they don't need a crisis but they've not prepared to take the steps for a real breakthrough".

The South made a concession before the Bali meetings, saying bilateral talks on nuclear issues could go ahead without the North's apology for two deadly border incidents last year.

"It's important the parties keep on talking to change the atmosphere to dialogue... talks will definitely have a positive influence," said Kim Yong-Hyun of Seoul's Dongguk University.

He said six-party talks were likely as early as September and would make progress -- but the North would press its demand to be accepted as one of the world's nuclear-armed nations.

Chang Yong-Seok, a senior researcher at the Institute for Peace Affairs, said six-party talks were highly likely to resume.

But the process would take some time since the two Koreas have only set aside, rather than resolved, issues such as the 2010 sinking of a South Korean warship and the North's artillery bombardment of a South Korean island.

A senior US official travelling with Clinton also cautioned that inter-Korean ties must improve. "Those who are suggesting that we are on the fast track to resumption of the six-party talks -- we need to see many more indications from the North Koreans before we approach that point."

Beck said the North sees its nuclear programme as a deterrent and realises that any "first-strike" use would bring devastating retaliation.

It might be willing to offer a freeze in the programme and a promise not to proliferate, perhaps in return for diplomatic relations with Washington and a peace treaty formally ending the 1950-53 war.