The closure of the Yongbyon nuclear plant, and the admission of UN nuclear inspectors, marked the first stage of a denuclearisation plan agreed to by envoys from the two Koreas, China, Japan, Russia and the US.

The second phase of the agreement calls for North Korea to declare and finally disable all its nuclear weapons programmes.

Ahead of the meetings, Christopher Hill, the chief US negotiator, said the working-group talks were not to negotiate an agreement but to sort out technical requirements so that an agreement could be put together.

Technical talks

"We're looking forward to a very good, a very substantive discussion," Hill said

"The purpose is not so much to negotiate an agreement today or this week but rather to identify the technical procedures that can be used to affect disablement."

He said the Shenyang talks aimed to build a "common understanding of technical tasks" ahead of a further meeting scheduled for September.

Shenyang is located about 200km from China's border with North Korea.

Progress on resolving the North Korean nuclear issue has gathered pace since a February agreement brokered by China.

Under the six-nation deal the North pledged to make a full declaration of all its nuclear programmes and disable them in exchange for energy assistance and diplomatic benefits.

Several recent developments have boosted optimism that, after months of delays and deadlock, progress may finally being made on the Korean peninsula.

Earlier this week Hill said after meeting Kim Kye-gwan, the North's chief negotiator, that the countries would soon begin discussions on normalising diplomatic relations.

Hill also said the US was considering providing aid to North Korea after floods left hundreds dead or missing and tens of thousands homeless.

Later this month the leaders of North and South Korea are due to hold only their second-ever summit meeting in Pyongyang, the North Korean capital.