The researchers projects the work could be completed by mid-2014.
New satellite images indicate that major construction work is underway at North Korea's missile launch station, a US think tank said Tuesday, while the US and China discussed resuming multinational talks to denuclearise the communist state.
In its analysis of commercial aerial photos taken Oct. 9, the US-Korea Institute at Johns Hopkins School of Advanced International Studies said that a second flat mobile missile launch pad may be under development in the western town of Dongchang, where the North successfully fired a long-range rocket in December. The researchers projected the work could be completed by mid-2014.
Also possibly under construction are two new bridges and a new road linking the area with the missile assembly building and Sohae railroad, it added. The existing Unha launch pad is apparently being upgraded to facilitate future tests of larger space launch vehicles.
"While it is too soon to reach a definitive judgment, evidence is growing that these activities are intended to support the two main priorities for North Korea's rocket programme launches of larger rockets and of new mobile missiles," the Washington-based think tank said on its website, 38 North.
"The new road has been strengthened and widened for use by heavy vehicles, possibly including transporter-erector-launchers for mobile missiles."
The analysis is the latest in a recent string of findings that pointed to potential developments of Pyongyang's nuclear programme.
SAIS and Seoul officials have also said that the rogue regime of Kim Jong-un had restarted a 5-megawatt reactor capable of generating plutonium for weapons, which could be used as another bargaining chip in its future nuclear negotiations with Washington.