The US hopes to achieve "major disarmament" by North Korea within the next few years, according to the country's secretary of state.
US Secretary of State Mike Pompeo has said Kim Jong-un understands that denuclearisation must happen "quickly", warning there will be no sanctions relief for Pyongyang until the process is complete.
Washington remained committed to the "complete, verifiable and irreversible" denuclearisation of North Korea, Pompeo added, after the historic US-North Korea summit in Singapore drew criticism for its vague wording on plans for Pyongyang to give up its nuclear weapons.
"We believe that Kim Jog-un understands the urgency... that we must do this quickly," he said on Thursday of the effort to have North Korea abandon its nuclear weapons.
Washington's top diplomat was in Seoul to brief his South Korean and Japanese counterparts after President Donald Trump's post-summit comments sparked confusion and concern in Tokyo and Seoul.
But Pompeo insisted at a joint press conference with the two countries' foreign ministers that there was no daylight among the allies on how to achieve the denuclearisation of North Korea.
Contrasting the Trump policy with previous US administrations, Pompeo said: "In the past, they were providing economic and financial relief before... complete denuclearisation had taken place. That is not going to happen, President Trump made that clear."
He also said the US hopes to achieve "major disarmament" by North Korea within the next 2.5 years, and there won't be sanctions relief before then.
Pompeo's comments came after North Korean state media reported Wednesday that Trump had not only offered to stop military exercises during dialogue, but also lift sanctions imposed on Pyongyang.
Trump said after his meeting with Kim - the first between sitting US and North Korean leaders - that Washington would halt its joint military exercises with South Korea, an announcement that caught Seoul - and apparently the Pentagon - by surprise.
The US and South Korea conduct several large drills every year to maintain readiness for operations on the peninsula, a source of irritation for Pyongyang, which considers them preparations for an invasion.
Kang Kyung-wha, the South Korean foreign minister appeared to sidestep the issue at the joint press conference, saying the matter would be left to military authorities to discuss, and that the US-South Korea alliance remained "as robust as ever".
Earlier, South Korean President Moon Jae-in acknowledged that "there may be very conflicting views" about the summit, but it had still helped mitigate fears of a nuclear war.