North Korea appears to have resumed excavation work at its underground nuclear test site, but the operations could be part of an attempt to camouflage preparations for a new nuclear test, the website 38 North said Wednesday.

Satellite imagery taken on April 19 shows what appear to be two small mine ore carts on the track crossing the road from the tunnel entrance of the West Portal to the spoil pile, which "suggests that tunnel excavation operations are about to resume, or have recently resumed, for the first time this year," 38 North said.

"Excavation operations can be undertaken concurrently with preparations for a nuclear test, as was the case during the run-up to this January's detonation. Such a concurrent activity could be part of the North's camouflage, concealment and deception procedures for the facility," it said.

38 North also said that the imagery shows limited vehicle and equipment activity at the North Portal, where the North's three recent nuclear tests took place, as well as at the Main Support Area.

"These activities by themselves do not establish that test preparations are imminent. However, the possibility of an impending test cannot be ruled out," it said.

"Pyongyang has clearly demonstrated, with its fourth nuclear detonation this past January, the ability to conduct detonations on short notice while masking indicators of its preparations from satellite view," it added.

Concerns have grown in recent weeks that Pyongyang could carry out yet another nuclear test after January's fourth test in an effort to project an image of Kim Jong-un as a strong leader in the lead-up to the Workers' Party Congress next month. (Yonhap)