America's top military officer has told his counterparts in South Korea that the United States is ready to use the "full range" of its military capabilities to defend itself and its allies from any North Korean provocation.
Marine Corps General Joseph Dunford, the chairman of the US Joint Chiefs of Staff, is visiting South Korea, Japan and China after a week in which President Donald Trump traded threats with North Korea.
Mr Trump had declared the US military "locked and loaded" and said he was ready to unleash "fire and fury" if North Korea continues to threaten America.
North Korea, meanwhile, has threatened to fire four intermediate-range missiles into the waters near Guam, a tiny US territory about 2,000 miles from Pyongyang, North Korea's capital.
This would be a deeply provocative act, from the US perspective, and there has been widespread debate about whether Washington would try to shoot the missiles down if they are launched.
The US-North Korean stand-off, which has simmered since the end of the Korean War in 1953, has grown more tense in recent months over worries that the North's nuclear weapons programme is nearing the ability to target the US mainland.
Pyongyang tested two intercontinental ballistic missiles last month.
Gen Dunford, who met with senior South Korean military officials and President Moon Jae-in, "stressed that North Korea's ballistic missile and nuclear weapons programs threaten the entire global community," according to US military spokesman Captain Darryn James.
"He conveyed America's readiness to use the full range of military capabilities to defend our allies and the US homeland," Capt James said.
Mr Moon separately called for a peaceful solution to the nuclear stand-off, saying that "there must not be another war on the Korean Peninsula".
In a meeting with top aides at the presidential Blue House, Mr Moon said South Korea would work to safeguard peace on the peninsula in co-operation with the United States and other countries.
Mr Moon said North Korea must stop issuing menacing statements.
North Korea, which is angry over new United Nations sanctions condemning its rapidly developing nuclear and missile programme, continued its tough stance on Monday.
The North accused the US of mobilising a huge number of weapons and troops for annual military drills with South Korea that begin later this month.
Pyongyang, which claims the drills are war preparation, said it will be ready to send its Guam missile launch plan to North Korean leader Kim Jong Un for approval just before the drills begin.
The North's official Korean Central News Agency said: "What matters is that if a second conflict (on the peninsula) erupts, that cannot help but lead to a nuclear war.
"We are closely monitoring every move by the United States."
The commentary said that about 3.5 million young students and workers have volunteered to join or rejoin the army because of a possible confrontation with the United States.
Gen Dunford earlier told reporters that he aims to "sense what the temperature is in the region". He also will discuss military options in the event the "diplomatic and economic pressurisation campaign" fails.
He said: "We're all looking to get out of this situation without a war."
Chinese president Xi Jinping talked to Mr Trump by telephone this weekend and called for cool-headedness.
Mr Xi urged Washington and Pyongyang to avoid words or actions that could worsen the situation.
Mr Trump has pushed China, North Korea's biggest economic partner and source of aid, to do more to stop the North's nuclear ambitions. Beijing insists its influence on Pyongyang is limited.
The US leader's recent threats followed a report that US intelligence indicates North Korea can now put a nuclear warhead on its long-range missiles.
For all his bluster, Mr Trump's words did not appear to be backed by significant military mobilisation on either side of the Pacific, and an important, quiet diplomatic channel remains open.
On Sunday, CIA director Mike Pompeo and Army Lt.Gen HR McMaster, Mr Trump's national security adviser, tried to provide assurances that a conflict is avoidable, while also supporting Mr Trump's tough talk.
They said the United States and its allies no longer can afford to stand by as North Korea pushes ahead with the development of a nuclear-tipped intercontinental ballistic missile.