Photo/Illutration This Dec. 19 satellite image from Planet Lab Inc. that has been analyzed by experts at the Middlebury Institute of International Studies, shows the March 16 Factory in Pyongsong, near Pyongyang, where North Korea manufactures military trucks used as mobile launchers for long-range missiles. This new satellite image shows the construction of a new structure this month. (Planet Labs Inc., Middlebury Institute of International Studies via AP)

SEOUL--A new satellite image of a factory where North Korea makes military equipment used to launch long-range missiles shows the construction of a new structure.

The release of several images from Planet Labs comes amid concern that North Korea could launch a rocket or missile as it seeks concessions in stalled nuclear negotiations with the United States.

North Korea has warned that what “Christmas gift” it gives the United States depends on what action Washington takes.

One of the new satellite images taken Dec. 19 shows the March 16 Factory near Pyongyang, where North Korea manufactures trucks used as mobile launchers for its long-range missiles.

Jeffrey Lewis, director of the East Asia nonproliferation program at the Middlebury Institute, tweeted that the construction appeared to be an expansion of the factory.

Nuclear talks between Washington and Pyongyang have been stalled since a February summit between leaders Donald Trump and Kim Jong Un fell apart.

Earlier this month, North Korea carried out two major tests at its long-range rocket launch and missile engine testing site in the country's northwest.

The other images released by Planet Labs show that site before and after the Dec. 7 test.