Iran is secretly negotiating with North Korea to build a network of underground bunkers to conceal its clandestine nuclear weapons project.

A team of construction experts has arrived in Teheran to conduct a survey of Iranian requirements. It included a senior North Korean specialist in underground construction who helped to design the bunkers that contain Pyongyang’s illegal weapons programme.

Current talks centre on whether the North Koreans will undertake the work for the Iranians, or act as advisers to Iranian construction companies.