BEIJING - Negotiators from six countries began Thursday to hash out exactly how they will verify North Korea's declaration of its nuclear materials, the U.S. envoy said.

The first round of six-nation talks in nine months comes after North Korea handed over the much-delayed list of materials last month, then blew up the cooling tower of its main reactor to demonstrate its commitment to disarmament.

"All and all, it was a good start to the process, but I think the effort to negotiate a verification protocol will be very important," U.S. Assistant Secretary of State Christopher Hill said.

He has said the actual verification process could take as long as several months.

The envoys have given the task of determining specifics of the verification process to a working group, Hill said.

Though there are basic agreements that the process would include site visits, interviews with North Korean officials and examination of documents, "there's a lot of technical issues there," he said.

"We can't say how quickly it will happen," Hill added.

South Korean envoy Kim Sook said Thursday's talks were held in a "serious and businesslike atmosphere." Negotiators also touched on details of a meeting for the foreign ministers of the six countries and future steps in the disarmament process, he said.

Meetings on Friday were expected to focus on the issue of economic and energy assistance for North Korea, Hill said.

The energy-starved North was promised fuel aid equivalent to one million tons of oil under the February 2007 deal. Japan has since opted out of contributing, citing a lack of progress by North Korea in resolving the issue of its abductions of Japanese citizens in the 1970s and '80s.

Pyongyang has complained that countries involved in the talks have supplied only 40 per cent of promised energy shipments.

In response to North Korea's nuclear declaration, the United States had announced it would remove the North from a list of state sponsors of terrorism and relax some economic sanctions against the communist nation.

The exchanges paved the way for the resumption of the six-nation meetings in Beijing. The talks also include host China, Japan and Russia.

"I want to emphasize that all of us ... gathered here share the same strategic objectives," China's nuclear envoy Wu Dawei said at the start of the talks Thursday. "The ultimate objective is the realization of a nuclear-free Korean peninsula."