North Korea is pressing ahead with a controversial launch of its Unha-3 long-range rocket, amid reports it is also planning a nuclear test.
Western journalists were invited to watch the rocket being moved into place in final preparation for the launch planned for this month, probably between 12 and 16 April.
The North says it is merely sending a weather satellite into space, but South Korea and the United States say it is a ballistic missile test.
At the same time, South Korean officials say satellite images suggest the North is preparing to carry out a third nuclear weapons test.
South Korea's Yonhap news agency quoted an unidentified intelligence source as saying commercial satellite images showed workers digging a tunnel in the northeastern town of Punggye-ri in addition to existing mines believed to have been used for tests in 2006 and 2009.
North Korea pulled out of six-party disarmament talks three years ago but agreed in February to stop nuclear tests, uranium enrichment and long-range missile launches in return for food aid.