But Pyongyang claims it is a peaceful centrepiece to celebrations marking the 100th anniversary of the nation’s founder.
The final preparations at the west coast launchpad were taking place as North Korea’s ruling Workers’ Party convened for a special conference.
Delegates are expected to further elevate new leader Kim Jong Un by giving him new titles, including some held by his father, the late Kim Jong Il.
The conference, being held at an undisclosed location in Pyongyang, is one of two major political gatherings this week that are expected to formally install the young Kim as North Korea’s supreme leader.
Two days after the political conference, the Supreme People’s Assembly will gather to ratify new legislation.
Such conferences also are watched closely for signs of changes in leadership. With two spots vacant on the Central Committee’s Political Bureau following the deaths of Kim Jong Il and a high-ranking military official, Kim Jong Un was among those anticipated to be promoted to standing member of the powerful policymaking body.
The events come as North Korea celebrates the April 15 centennial of the birth of Kim Jong Un’s grandfather, Kim Il Sung, a major milestone in the nation he founded in 1948.
North Korea has thrown open its doors to a select group of journalists and visitors from abroad for two weeks of celebrations in what might be the largest influx of foreigners in years.
North Korea also marks the 80th anniversary of the founding of the Korean People’s Army, another key event, on April 25.