The arrest by Japanese police this week of three men over an alleged attempt to send high-tech arms-making equipment to Burma at the behest of North Korean agents has deepened suspicions that Pyongyang is helping to arm Burma’s military junta.

Evidence of co-operation between the two pariah states has mounted in recent weeks. A US warship has been trailing a North Korean vessel believed to be carrying small arms to Burma in violation of UN sanctions, while Burmese exiles have published photographs of underground tunnels and bunkers that they said were built inside Burma with North Korean help.