US Vice-President Mike Pence has said his country and South Korea are in complete agreement on the need to maintain pressure on North Korea.
Speaking on his way home from the Winter Olympics in South Korea, Mr Pence said there was "no daylight" between the two allies on the issue.
The Games has seen better ties between the two Koreas despite tensions over the North's nuclear programme.
But the US has distanced itself from the North Korean overtures.
On Saturday North Korean leader Kim Jong-un invited the South's President, Moon Jae-in, to Pyongyang for talks.
It would be the first summit in more than a decade between Korean leaders. Mr Moon said the Koreas should "make it happen" and encouraged the North to return to negotiations with the US.
However, his Prime Minister, Lee Nak-yeon, said on Sunday he hoped "the right conditions" would be created for the summit to be held, with support from the international community. He did not specify what conditions he had in mind.
Pyongyang's nuclear programme is expected to hang over any attempts to bring the countries closer together.
The US administration has sought to maintain pressure on North Korea through sanctions and tough rhetoric from President Donald Trump.
Speaking to reporters during a flight on Saturday, Mr Pence said: "There is no daylight between the United States, the Republic of Korea and Japan on the need to continue to isolate North Korea economically and diplomatically until they abandon their nuclear and ballistic missile programme."
The handwritten invitation to President Moon was delivered by Mr Kim's influential sister, Kim Yo-jong, at a landmark meeting in the presidential palace in Seoul, as the Games opened on Saturday.
Ms Kim and the North's ceremonial head of state Kim Yong-nam made up the most senior delegation from the North to visit the South since the Korean War in the 1950s.
How the move could drive a wedge between allies
The invitation puts Mr Moon in a difficult position as he had promised to engage with the North, but his US ally is cautious of Seoul falling for North Korea's charm offensive.
Despite the public shows of friendliness, experts have warned the underlying tensions have not gone away.
At the opening ceremony for the Games, Mr Pence, Kim Yo-jong and Kim Yong-nam were seated in close proximity to each other.
Mr Pence stayed seated when South and North Korean athletes marched together under a unified flag, and also skipped a dinner with the North Korean delegation.
In a tweet, he reasserted the sceptical view taken his administration regarding recent conciliatory gestures by North Korea.
Well said, @AmbJohnBolton. The U.S will not allow the propaganda charade by the North Korean regime to go unchallenged on the world stage. The world can NOT turn a blind eye to the oppression & threats of the Kim regime. pic.twitter.com/PPtiPpeMNI— Vice President Mike Pence (@VP) February 10, 2018
Kim's sister takes the stage
The Winter Olympics has thrust Kim Yo-jong into the spotlight.
The highest-profile member of the North Korean delegation to the Games, she is the first immediate member of the North's ruling family to visit the South since the 1950-1953 Korean war.
Ms Kim, who is though to be about 30 years old, was promoted to the powerful politburo last year. She is on a US sanctions list over alleged links to human rights abuses in North Korea.
Later on Saturday Ms Kim, Kim Yong-nam and Moon Jae-in attended the first ice hockey match played by a unification team of athletes from both North and South Korea.
They were beaten by Switzerland 8-0