Donald Trump says that North Korea is “behaving badly and it’s got to stop”.
Speaking at a White House news conference, the US President said he would prefer not to use military action against the nuclear state but warned “nothing is inevitable”.
He said: “Each new day equipment is delivered, new and beautiful equipment, the best in the world.
“The best anywhere in the world, by far.
“Hopefully, we’re not going to have to use it on North Korea.
“If we do use it on North Korea, it will be a very sad day for North Korea.”
His words come just days after North Korea tested what the US believes was a thermonuclear or hydrogen bomb.
A senior official said the US administration is “assessing” the test, adding: “So far there is nothing inconsistent with the North Korean claim that this was a hydrogen bomb, but we don’t have a conclusive view on it yet.”
His options for responding to the latest test are limited: Any attack would provoke a brutal counter-attack from North Korea, which would put millions of people in the South Korean capital of Seoul at risk.
Defence Secretary James Mattis said last week: “We are never out of diplomatic solutions”, perhaps in recognition that military options are restricted.
Mr Trump has tried to convince China to exert more pressure on its neighbour and major trade partner.
China’s foreign minister said on Thursday that his country wants to see renewed efforts to start talks involving all sides and that it supports further action from the United Nations.
Wang Yi said China hopes North Korea would “see the situation clearly and come to the right judgement and choice”.
Chinese President Xi Jinping joined German Chancellor Angela Merkel in calling for tougher sanctions against North Korea.
Mr Xi said: “Facts have repeatedly proven that the Korean Peninsula issue can only be resolved through peaceful means, including dialogue and consultation.
“This requires the international community to work together.”