The top US military commander in the Pacific has said that America wanted to bring Kim Jong-un "to his senses" as he warned North Korea could strike American soil.
It came as the Trump administration announced a tightening of sanctions against North Korea and a stepping up of diplomatic efforts amid mounting tensions over Pyongyang’s nuclear threats.
Admiral Harry Harris, who heads the US Pacific Command, defended the deployment of the Terminal High Altitude Area Defence (THAAD) missile defence system in South Korea.
He told Congress that he believed North Korea's threats against the US needed to be taken seriously.
"I don't share your confidence that North Korea is not going to attack either South Korea, or Japan, or the United States ... once they have the capability," he said.
"In confronting the reckless North Korean regime, it's critical that we're guided by a strong sense of resolve, both privately and publicly, both diplomatically and militarily," he said.
North Korea's UN Mission said on Wednesday the government would react to "a total war" with the United States with a nuclear war.
Pyongyang will "surely win a victory in the death-defying struggle against the US imperialists," a statement said.
The Democratic People's Republic of Korea "can never be frightened" by the Trump administration's effort to bring the country "into submission" by deploying a nuclear aircraft carrier strike group to waters off the Korean Peninsula, it continued.
North Korea's youth league said young supporters were preparing to "wipe out" the US and South Korea with five million nuclear bombs, according to the state-run news agency.
Boris Johnson, the Foreign Secretary, last night said Mr Kim was leading a "semi-deranged regime in North Korea, bent on getting nuclear weapons that could one day be used to strike this country".
After briefing senators in a highly unusual meeting at the White House, Pentagon chief Jim Mattis, Secretary of State Rex Tillerson and Director of National Intelligence Dan Coats issued a statement that toned down military rhetoric and urged the international community to help find a solution to North Korea's nuclear threats.
President Donald Trump aims to "pressure North Korea into dismantling its nuclear, ballistic missile, and proliferation programs by tightening economic sanctions and pursuing diplomatic measures with our allies and regional partners," the statement read.
"We are engaging responsible members of the international community to increase pressure on the DPRK in order to convince the regime to de-escalate and return to the path of dialogue," the statement added, using North Korea's official name.
Mr Trump has been urging China to force North Korea to abandon its nuclear weapons programme. Some observers believe Washington aims to exert more pressure on China by heightening concerns that a conflict could break out.