The official, who was speaking on condition of anonymity, also said that North Kotrea had conducted at least two engine combustion tests since January.
“Taking into account the scope of the tests, the new rocket will be larger than Unha-3 and it will have a range of about 10,000 kilometers,” he added.
North Korea has erected a launch pad capable of firing long-range missiles larger than those of the past, South Korean media reported on Wednesday.
Pyongyang began work in late 2013 to extend its 50-meter-tall launch pad in Dongchang-ri, North Pyongan Province, near the border with China. It appears to have nearly finished the work to make the launch pad 67 meters tall, a government source, speaking on condition of anonymity, told Yonhap news agency.
Military and intelligence officials believe the new launch pad is now capable of firing long-range missiles twice the size of the 30-meter-long Unha-3, which was used to put a satellite into orbit in December 2012.