Tokyo  - North Korea should submit written confirmation to allow inspections of its nuclear facilities, the chief negotiators of Japan, the US and South Korea said Wednesday.

Japanese representative Akitaka Saiki, US envoy Christopher Hill and South Korea's Kim Sook said in Tokyo that a written commitment was needed to allow the taking of samples at various sites.

They also insisted that all nuclear sites and related facilities be included, according to the members of the six-party talks that also include China, Russia and North Korea.

Hill expressed his hope for progress in the next round of talks due to start Monday in Beijing, although China had not officially confirmed the meeting yet.

The preparatory talks between the US, South Korea and Japan had been helpful in preparing a proposed solution, Hill said.

The issue of sample-taking has been at the centre of controversy since North Korea denied last month that such inspections were part of a deal on verification procedures agreed in October.

On November 12, North Korea's foreign ministry called a US demand for environmental and waste samples a breach of sovereignty that would "certainly bring about a war." (dpa)