US Secretary of State Mike Pompeo says he is ready to restart negotiations with Pyongyang, with the aim of denuclearising North Korea "by 2021".
Discussions between the two sides had stalled following a broad-strokes agreement made earlier this year.
But this week's inter-Korean summit saw the North's Kim Jong-un agreeing to shut a major missile launch site.
South Korean President Moon Jae-in also gave an unprecedented speech in front of tens of thousands of North Koreans.
Mr Kim "agreed on a way to achieve denuclearisation" on the Korean peninsula following the summit with his South Korean counterpart, Moon Jae-in.
Mr Pompeo said it was "on the basis of these important commitments" that the US was "prepared to engage immediately in negotiations".
In a statement, he said he had invited North Korean Foreign Minister Ri Yong-ho to meet him in New York next week, while invitations had been extended for a second meeting between North Korean and US representatives in Vienna, Austria.
"This will mark the beginning of negotiations to transform US-DPRK [North Korea] relations through the process of rapid denuclearisation of North Korea, to be completed by January 2021, as committed by Chairman Kim, and to construct a lasting and stable peace regime on the Korean Peninsula," he said.
The January 2021 date is the most specific timeline an official on either side has put forward publicly so far.
What happened at the summit?
The main focus of the summit between Mr Kim and Mr Moon was the issue of denuclearisation.
Mr Kim expressed a readiness to shut down the Yongbyon nuclear facility - where North Korea is believed to have produced the material used in its nuclear tests - if the US takes some reciprocal action.
The BBC's Laura Bicker in Seoul says that is likely to be the US signing a peace treaty to formally end the Korean War.
But he went further on Tongchang-ri, saying the engine missile testing and launch facility would be permanently closed "in the presence of experts from relevant nations". Our correspondent say that is a major step forward.
Satellite images suggest Tongchang-ri is in the process of being destroyed, she adds, but the declaration will allow inspectors to verify the process.
- Tongchang-ri has been North Korea's main satellite launch facility since 2012, according to monitoring group 38 North.
- It has also been used for testing engines for North Korean missiles capable of reaching the US.
- Read more on North Korea's missile and nuclear programme
North Korea blew up its main nuclear testing site at Punggye-ri shortly before Mr Kim's meeting with US President Donald Trump in June.
On Thursday, the two leaders of North and South embarked on a trip to Mount Paektu which holds a central place in Korean mythology. The volcano is situated at the border between the North and China.
What does this mean for US?
Mr Trump welcomed the agreements, which he said were "tremendous progress", and was quick to tweet his applause for the Moon-Kim summit.
Kim Jong Un has agreed to allow Nuclear inspections, subject to final negotiations, and to permanently dismantle a test site and launch pad in the presence of international experts. In the meantime there will be no Rocket or Nuclear testing. Hero remains to continue being........— Donald J. Trump (@realDonaldTrump) September 19, 2018
....returned home to the United States. Also, North and South Korea will file a joint bid to host the 2032 Olympics. Very exciting!— Donald J. Trump (@realDonaldTrump) September 19, 2018
The US and North Korea held their own historic meeting in June when Mr Trump and Mr Kim agreed in broad terms to work towards denuclearisation.
Since then, however, there has been little progress, with no clear process nor timeline laid out, while an abruptly cancelled trip to Pyongyang by Mr Pompeo in August led to speculation relations had soured somewhat.
Most observers warn that so far the North has taken no meaningful steps to end its controversial nuclear weapons programme and that this week's summit might not be enough to convince them otherwise.
But Mr Trump has remained confident of the North Koreans' commitment, recently saying that he and Mr Kim would "prove everyone wrong", after he received an invitation from the North Korean leader for a second summit. Both sides say they are working on making that meeting happen.