Talks aimed at normalising diplomatic relations between the US and North Korea for the first time in more than 50 years have opened in New York.
North Korea is due to shut down its Yongbyon nuclear reactor
The two-day meeting comes just three weeks after North Korea agreed to abandon part of its nuclear programme.
On the agenda is the US designation of North Korea as a terrorist state as well as possible lifting of sanctions.
Bilateral talks with the US have long been a condition set by the North for abandoning its nuclear ambitions.
Analysts describe it as a breakthrough in efforts to end years of feuding since the US led an international force against the North in the 1950-1953 Korean War.
'Fruitful and friendly'
Taking part are the US Assistant Secretary of State, Christopher Hill, and the North Korean Deputy Foreign Minister, Kim Kye-gwan - the two countries' top nuclear negotiators.
Neither of the men spoke to the media after an initial meeting followed by dinner on Monday. The two are expected to hold a full day of discussions on Tuesday.
The talks are a sign relations between the countries are thawing
Earlier on Monday Mr Kim visited the Korea Society, a non-profit organisation that promotes greater understanding and cooperation between Americans and Koreans.
He spent more than four hours with academics and VIPs including former US secretaries of state Henry Kissinger and Madeleine Albright.
Mrs Albright told reporters: "We had a very good and fruitful and friendly meeting."
The BBC's Laura Trevelyan in New York says the meeting is a significant sign that relations between the two countries, frosty for so long, are thawing at least a little.
US President George W Bush labelled North Korea part of the "axis of evil" in 2002.
Last year North Korea carried out an underground test of a nuclear weapon provoking widespread condemnation by global leaders.
In recent months Washington has refused one-on-one debates with North Korea, preferring to hold multi-party talks with South Korea, Japan, Russia and China.
It was at such talks last month in Beijing that North Korea agreed to dismantle its nuclear programme in exchange for economic aid.
The two nations are now talking and analysts say the US will seek assurances that Pyongyang is committed to following through on the nuclear deal.
Under the agreement North Korea will receive 50,000 tonnes of fuel oil for shutting down its Yongbyon facility, which produces enough plutonium for one atom bomb each year.
Another 950,000 tonnes of oil have been promised once the reactor has been permanently disabled and international inspectors allowed access.
Senior US official John Negroponte has arrived in South Korea for talks expected to focus on how to enforce the nuclear deal.
The head of the UN nuclear watchdog, the International Atomic Energy Agency, Mohamed ElBaradei, is to travel to North Korea next week to discuss ways of monitoring dismantled facilities.