The US envoy to the United Nations has said North Korean leader Kim Jong‑un is "begging for war" with his latest and most powerful nuclear bomb test.
Nikki Haley told an emergency meeting of the Security Council in New York that America did not want a war but its patience was "not unlimited".
The US will table a new UN resolution shortly to toughen sanctions.
China, the North's main ally, has called for a return to negotiations and Switzerland has offered to mediate.
South Korea carried out live‑fire exercises on Sunday, simulating an attack on the North's nuclear test site.
German Chancellor Angela Merkel said she would press for tougher EU sanctions on North Korea, agreeing with US President Donald Trump by phone on the need for stricter measures.
Japan is planning, in the event of war, for a mass evacuation of nearly 60,000 Japanese citizens currently living in or visiting South Korea, Nikkei Asian Review reports.
