US Vice-President Mike Pence is to give security reassurances to allies in Asia amid growing tensions over North Korea's missile and nuclear programmes.
On a visit to South Korea, he is set to discuss ways to deal with Pyongyang amid speculation that leader Kim Jong-un could order a new nuclear test.
North Korea has warned the US not to take provocative action as it is "ready to hit back with nuclear attacks".
A US navy strike group is moving towards the Korean peninsula.
On a long-planned 10-day trip to Asia, his first official visit to the region, Mr Pence will reaffirm the US commitment to stand by its regional allies, officials say.
It comes as Washington steps up the pressure on the isolated North, with President Donald Trump saying that the United States is ready to act alone to deal with the nuclear threat.
Mr Pence's visit comes a day after North Korea displayed what appeared to be new intercontinental and submarine-launched ballistic missiles during a huge military parade in Pyongyang.
On display for the first time were what appeared to be the Pukkuksong submarine-launched ballistic missiles (SLBMs), which have a range of more than 1,000 km (600 miles).
Weapons analysts said there also appeared to be two new types of intercontinental ballistic missiles (ICBM) in canister launchers. But it remains unclear whether they have been tested and Pyongyang has yet to announce it has an operational ICBM.
The nation's aim is to be able to put a nuclear warhead on an ICBM that can reach targets around the world.
It has conducted five nuclear tests and a series of missile launches in pursuit of that goal.
Pyongyang has claimed to have miniaturised nuclear warheads for use on missiles, though experts have cast doubt on that given the lack of evidence.
The military parade in Pyongyang marked the 105th anniversary of the birth of North Korea's founding president, Kim Il-sung.
During the large event, Choe Ryong-hae, believed to be the country's second most powerful official, issued a warning to the US.
"We're prepared to respond to an all-out war with an all-out war... We are ready to hit back with nuclear attacks of our own style against any nuclear attacks."
Meanwhile, the aircraft carrier USS Carl Vinson and an accompanying battle group are steaming towards the region, a deployment seemed to be a show of strength.
US officials were quoted by the Associated Press news agency as saying that the Trump administration was focusing more on raising pressure on North Korea with the help of China rather than using military force.