Analysis published Sunday of recent satellite images fuelled concerns that North Korea may be on the brink of another nuclear test or long-range rocket launch.

Speculation that Pyongyang is preparing such a show of force has been linked to Monday's anniversary of the founding of the North's ruling Workers' Party.

Past nuclear tests and missile launches have often coincided with key political dates. Its fifth nuclear test last month was conducted on the anniversary of North Korea's founding as a state,

The latest satellite imagery analysis posted by the US-Korea Institute at Johns Hopkins University noted increased activity at the North's Sohae satellite launch station.

The pictures taken on October 1 showed crates on the launch pad next to the gantry tower, vehicles near the fuel and oxidiser buildings, and work continuing on the facility's vertical engine test stand.