The NGO is calling on the US to withdraw nuclear warheads it stores in Germany.
State media outlet KCNA said it boosted the country's strategic nuclear deterrence. South Korea's defence minister said it was an engine test.
North Korea's chief nuclear negotiator, Kim Myong Gil, blamed the US for their inflexibility, saying the negotiators from Washington would not "give up their old viewpoint and attitude."
Russia honours 'national heroes' killed in mysterious rocket blast
Nagasaki Mayor Tomihisa Taue said Japan had a responsibility to sign a nuclear treaty ban and maintain a "philosophy of peace" within the nation's constitution
"We are no longer in the classic strategy of deterrence by accumulation of nuclear warheads," a SIPRI expert told Euronews. "Now they have embarked on a tactical war."
South Asia is a nuclear flashpoint, expert tells Euronews
A Russian state TV news show has named a list of targets in the US it claims Moscow would aim to destroy in the event of a nuclear confrontation.
The activists are calling for the removal of nuclear weapons from Europe.
The US and Russia have abandoned the 1987 INF treaty that prevented both countries from developing nuclear missiles.
Vladimir Putin’s claim that Russian victims of a foreign nuclear strike would go to heaven as martyrs has sparked a bizarre stunt in an aptly-named Russian city.
The US Secretary of State has invited North Korea’s foreign minister for talks next week and aims to achieve denuclearisation by 2021.
As a next step, North Korea will allow experts from "concerned countries" to watch the its closure