South Korean President Moon Jae-in has called on his US ally to help prevent a war, amid worsening tension over the North’s nuclear threat.
Mr Moon told the visiting top US military official that there must be a diplomatic solution to the crisis.
Gen Joseph Dunford said the US priority was diplomacy but he added that it was committed to defending the South against a possible military attack.
The North on Monday said any war could “only be turned into a nuclear war”.
In another development, Ukraine has denied supplying North Korea with rocket engines from one of its factories.
US President Donald Trump has warned North Korea against threatening the American territory of Guam. The US has 28,500 troops in South Korea.
Speaking on Monday, Mr Moon said: “Our top priority is the national interest of [South Korea] and our national interest lies in peace.
“I am confident that the US will respond to the current situation in a calm and responsible manner in line with our policy direction.”
He urged the North to “stop all provocations and hostile rhetoric immediately, instead of worsening the situation any further”.
Gen Dunford, chairman of the US Joint Chiefs of Staff, said after meeting Mr Moon that the US sought a peaceful resolution to the crisis with the North.
“Our job is to make sure our leadership has an option available to them,” he added, as quoted by South Korea’s Yonhap news agency.
“I believe there are two things we are clear about: one, our responsibility to defend against attack, two, our requirement to make sure we have a decisive response in the event of attack.”
The US, he said earlier, had “viable military options in the event that the diplomatic and economic pressurisation campaign fails”.
The general is due to travel on to China and Japan.
The North’s news agency, KCNA, warned on Monday that a conflict could be sparked by “a minor incident”.
“The problem is that if the war occurs, it can only be turned into a nuclear war,” it said.
