South Korean truck drivers walk to get in their trucks at the  inter-Korean Kaesong Industrial Complex. Pyongyang has previously threatened to close the border industrial zone, the last remaining example of inter-Korean cooperation which gives the North access to $2 billion in trade a year. Photograph: Lee Jae-Won/Reuters

North Korea said it had "ratified" a merciless attack against the United States, potentially involving a "diversified nuclear strike". "(...)