North Korea's new top envoy sat down with his Chinese counterpart Monday with relations between the secretive state and its historic benefactor on edge as Pyongyang stubbornly pursues its internationally condemned nuclear programme.

Foreign Minister Ri Yong-Ho, a career diplomat and party princeling, was making his first appearance at a major diplomatic gathering in his new role in the capital of fellow communist Laos.

Washington's top diplomat John Kerry also held talks with linchpin ally South Korea in Vientiane, with both sides describing relations as closer than ever in the face of Pyongyang's sabre-rattling.

"This is the right time for us to send out a very clear and strong message to North Korea that our alliance is stronger, deeper and broader than ever," Seoul's Foreign Minister Yun Byung-Se after a sitdown with Kerry.

Little emerged from Ri's meeting with his Chinese counterpart Wang Yi.

"The meeting was held as part of the two countries' normal communication process," an unnamed North Korean official said after the sitdown.

Both Beijing -- North Korea's main diplomatic protector and economic backer -- and Pyongyang share a deep suspicion of Washington's strong presence in the region.

But China has grown impatient with North Korea's refusal to reign in its weapons programme after its fourth nuclear test in January and a series of missile launches this year sparked international uproar.

Pyongyang's repeated provocations has pushed tensions on the Korean peninsula to a new high, and finally led Washington and Seoul to announce earlier in July the long-discussed deployment a US missile defence system in South Korea to counter the threat from the North.

- Mixed messages -

The United States spearheaded the drafting of a new toughened UN sanctions against Pyongyang in response to this year's barrage of weapons tests, which were adopted unanimously in March by Security Council members, including China.

Washington has also urged China to use its leverage over Pyongyang to implement the tougher sanctions and push the reclusive state towards bankruptcy.

But Beijing is wary of pushing the North too far, fearing a regime collapse that could create a refugee crisis on its border and swing the regional balance of power towards the United States.

Ri, 59, was previously North Korea's chief nuclear negotiator at the long-stalled, six-party talks aimed at halting the hermit state's weapon's programme.

His new appointment in May was seen as a signal that Pyongyang wanted to ease its international isolation.

But Pyongyang has continued its provocations with a series of missile tests.

That has prompted Seoul and Washington to announce plans for a missile defence shield to be deployed in South Korea by the end of next year.

Those moves have riled China and Russia.

Japan is also in the Laos capital this week, a rare moment when all members of the six party talks are in the same room.

The US is due to hold sideline talks with China and Russia, but US officials said a meeting with Pyongyang's envoy is highly unlikely.