'Clear roadmap'

Speaking ahead of the talks, Hill said his meetings with North Korean officials would focus on establishing a clear protocol for verifying disarmament.

"When we get to verification we want to have a clear roadmap of how verification is being done," he told reporters earlier after arriving in Singapore from Tokyo.

"We don't want a situation where, when we get to verification, there is some misunderstanding on what we agreed to."

After reaching an apparent agreement on verification procedures, the US announced it would drop the North from the so-called "terrorism blacklist". The North then reversed its plans to restart its plutonium-producing nuclear plants.

However, North Korea, which tested a nuclear weapon in October 2006, insists it never agreed to samples of atomic material being taken away from its nuclear sites.

Pyongyang says the outside verification of its nuclear inventory, submitted in June, will involve only field visits, confirmation of documents and interviews with technicians.