Experts caution that military intervention in North Korea remains unlikely - at least for now.
Mr Ely Ratner, a senior fellow for China studies at the Council on Foreign Relations, said President Donald Trump's language was "irresponsible", but did not think "we are on the brink of nuclear war", adding that "there is very little indication that what the President said reflects an actual policy decision within the White House to pursue pre-emptive war".
Still, the Pentagon has detailed plans for a potential conflict with North Korea and has spent decades rehearsing some of these with South Korean counterparts.
Options range from limited surgical strikes on nuclear targets to a pre-emptive "decapitation" attack to take out Mr Kim Jong Un or force a popular uprising that would lead to regime change. But any sort of military confrontation against a country that has more than one million serving troops would carry enormous risks.
CHINA, ECONOMIC PRESSURE
The United Nations Security Council last weekend passed a new set of sanctions against Pyongyang over its weapons programme, including bans on the export of coal, iron and iron ore, lead and lead ore as well as fish and seafood. They were approved unanimously - including by China, the North's sole major ally.
Their fate hinges largely on China, which accounts for 90 per cent of trade with North Korea but is suspected of failing to enforce past UN measures.
THE NEGOTIATING TABLE
North Korea has reportedly produced a nuclear warhead small enough to fit on its rockets, leading some to say the time for military action has already passed.
"There is no room for anything else other than diplomacy," said Dr Jeffrey Lewis, arms control expert at the Middlebury Institute of International Studies. "The window to attack them or convince them not to (develop the weapons) has closed."
Six-party talks in the 2000s involving China, the two Koreas, the US, Japan and Russia collapsed in 2009.