"We have been here before but continue to monitor the situation carefully," Johnson said in a statement.
"We stand alongside our international partners in making clear that North Korea must adhere to UN resolutions designed to secure peace and stability in the region and stop its pursuit of nuclear weapons."
The nuclear-armed state is under United Nations sanctions over its weapons programmes.
It has carried out five nuclear tests –- two of them last year -– and multiple missile launches, one of which saw several rockets come down in waters provocatively close to Japan last month.
North Korea's weapons of war rolled through Pyongyang on Saturday and a senior figure in the regime said it could "beat down enemies with the power of nuclear justice", as leader Kim Jong-Un mounted a spectacular show of strength.
Ostensibly Saturday's event was to mark the 105th anniversary of the North's founder Kim Il-Sung's birth -- a date known as the "Day of the Sun".
But it was also intended to send an unmistakable message to Washington about the isolated country's military might.
Tensions over North Korea's nuclear ambitions are stretched to the limit, with US President Donald Trump deploying an aircraft carrier battle group to the region.
Speculation that Pyongyang could conduct a sixth blast in the coming days to coincide with the anniversary has reached fever pitch, with specialist US website 38North describing its Punggye-ri test site as "primed and ready" and White House officials saying military options were "already being assessed".
WATCH: Bob Carr on China's North Korea influence
