The sparse base, which is under a square mile in size, was used in April to test-launch a rocket capable of reaching the west coast of the United States.
An unnamed South Korean government official told the Chosun Ilbo newspaper that North Korea will probably launch another long-range missile from the site as early as mid-June, in its latest act of aggression. US satellite photos have also picked up increased activity at the base, and the North Korean military has reduced its communication to essential messages only in order to foil eavesdroppers.
However, other experts cautioned that it will take longer than two weeks to assemble the missile and fuel it. North Korea's Taepodong-2 missile has a range of almost 4,200 miles.
The Communist state defied the United Nations and carried out an underground nuclear explosion last week, before peppering its coastal waters with a number of short-range missiles.
The UN Security Council, which unanimously condemned the nuclear test, is still considering its response to the crisis, with America pushing for tougher sanctions against Pyongyang. James Steinberg, the deputy US secretary of State, is touring Tokyo, Seoul, Beijing and Moscow this week to discuss the situation.
US officials confirmed to the Financial Times that North Korea is moving a new missile, but cautioned that Pyongyang might be engaging in deception to win further bargaining points.
The US Defence department has said it is capable of intercepting North Korean missiles. The rogue state also does not have the technology to mount a nuclear warhead onto the Taepodong 2.
In a further sign of its aggressive intent, North Korea has prohibited vessels from sailing in the mid and upper parts of the Yellow Sea until the end of July. Although bans on sailing in the area are issued frequently by Pyongyang, the latest embargo is unusually long in duration. South Korea said it was monitoring activity in the area very carefully.
Illegal Chinese fishing boats have already pulled out of the area, with their numbers dropping from 280 to 120 since last Thursday.
Meanwhile, two American journalists, arrested by North Korea nearly three months ago while they were working on a story on its northern border, are due in court this week. Laura Ling and Euna Lee will be charged with "engaging in hostile acts" and could be sent to a labour camp. The two women will stand trial on June 4.
"Having two journalists detained in the North leaves the US very little manoeuvring room [in its negotiations] since Washington now has to take the women's safety into account," said Yoon Deok-min, a professor at South Korea's Institute of Foreign Affairs and National Security.