Major construction has begun at the rocket launch site North Korea used last year to launch a satellite, a U.S. research institute says. The U.S.-Korea Institute at Johns Hopkins University School of Advanced International Studies said on its 38 North website, which deals with North Korea, expansion work is under way at North Korea\'s Seohae Satellite Launching Station in Tongchang-ri. The site is in the northwest part of the country near the Yellow Sea, about 31 miles from the Chinese border city of Dandong, The Wall Street Journal reported. The Journal said the institute used satellite images taken earlier this month for its analysis. Analyst Nick Hansen said the construction involves an additional flat mobile missile launch pad and a wider road to be used for heavy vehicles. He said the new road can be used by transporter-erector-launchers. Additionally, work is going on at the launch gantry, last used for December\'s satellite-launch vehicle, which may indicate preparation for more satellite launches. The completion of the satellite launch pad upgrade could allow \"Pyongyang to proceed with another space launch should it decide to do so,\" Hansen said. North Korea\'s December launch using the Unha-3 rocket was in violation of United Nations sanctions. International experts said it was actually a test of the isolated communist country\'s ballistic-missile-launch technology although North Korea claimed it was for launching a satellite.