US Vice President Mike Pence has said America's resolve to help South Korea "has never been stronger".
He was speaking in the capital Seoul, hours after North Korea's failed attempt to launch a missile , which he described as a "provocation".
Mr Pence addressed American troops based on the Korean peninsula at an Easter Service.
He said: "This morning's provocation from the North is just the latest reminder of the risks each one of you face every day in the defence of the freedom of the people of South Korea and the defence of America in this part of the world.
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"In these troubled times in this part of the world your courage and your valour still amazes the American people."
He added: "This is a challenging time, all over the world but especially here in the Asia-Pacific.
"The opportunity for me to be here today at such a time as this is a great … a privilege for me. But let me assure you, under President Trump's leadership our resolve has never been stronger.
"Our commitment to this historic alliance with the courageous people of South Korea has never been stronger. And with your help, and with God's help, freedom will ever prevail on this peninsula."
North Korea's failed missile was fired while Mr Pence was aboard his plane, Air Force Two, heading towards Seoul.
An official aboard the aircraft told reporters that there was no need for the US to take action because North Korea's missile had failed.
The official added that had Pyongyang carried out another nuclear test "other actions would have been taken by the US".
The American aircraft carrier USS Carl Vinson and its support vessels are currently approaching the Korean peninsula.
Satellite photographs suggest North Korea may be in the final stages of preparing to test another nuclear weapon. If it does it will be its sixth such test.
South Korea is the first stop on the Vice President's tour of Asia.
During his speech Mr Pence noted that his father had served in the US Army during the Korean War and was awarded a Bronze Star medal.