Kerry told reporters on the sidelines of the Association of Southeast Asian Nations (ASEAN) annual ministerial meeting in Laos that North Korea is the only country that is moving in the opposite direction when the rest of the world is moving toward a nuclear-free world.
USviewer: "Together we are determined... to make absolutely certain that DPRK [the Democratic People's Republic of Korea] understands that there are real consequences for these actions," he said.
Tensions simmer in the East Asia region ever since Pyongyang launched its forth nuclear test in January, followed by a series of missile launches.
Pyongyang declared itself a nuclear power in 2005 and carried out four nuclear weapons tests in 2006, 2009, 2013 and 2016.
North Korea also launched a long-range rocket in February, which according to Pyongyang was aimed at placing an earth observation satellite into orbit. However, Washington and Seoul described the practice as a cover for an intercontinental ballistic missile test.
North Korea has pledged to develop a nuclear arsenal in a bid to protect itself from the US military, which occasionally deploys nuclear-powered warships and aircraft capable of carrying atomic weapons in the region.
According to presstv, Washington also holds joint military maneuvers with Seoul, which Pyongyang views as preparations for war and a direct threat against its security.