Countries hold first talks since Kim Jong-il's death in Beijing, in effort to restart wider six-nation negotiations.
Envoys from the United States and North Korea have met in Beijing for their first talks on dismantling Pyongyang's nuclear programme since the death of Kim Jong-il, the country's long-time leader.
The discussions, which started on Thursday, will be closely watched for signs of a more co-operative approach from North Korea, which stands to gain food and economic aid in return for taking steps to end its efforts to develop nuclear weapons.
Kim's death on December 17 last year stalled talks that officials said were close to concluding a deal on the US providing food aid in return for the suspension of uranium enrichment activities.
"Today is, as we say, 'game day'. We will have an opportunity to meet with First Vice Foreign Minister Kim and his team," Glyn Davies, the US envoy, said before the start of morning talks on Thursday with Kim Kye Gwan at the North Korean Embassy in Beijing.
The two will hold a second session of meetings on Thursday afternoon at the US embassy.
The talks in Beijing are the third round of negotiations since July, and are aimed at restarting wider six-nation disarmament talks, which also involve China, Japan, Russia and South Korea.
Those talks have been suspended since 2009, when North Korea walked away from the table, and later exploded its second nuclear device.
The US has insisted that any progress on providing aid will be tied to North Korea improving relations with neighbour to the south, South Korea, which is a key US ally.
The North has rejected South Korean offers to return to the negotiating table in recent weeks, and tensions remain high on the Korean peninsula following violence in 2010, when a North Korean artillery attack killed four South Korean soldiers and a South Korean warship was sunk.
Davies said that it was a positive sign that Pyongyang had agreed to restart talks so soon after Kim's death, amid a power transfer to his son, Kim Jong-un.
Davies said that a key point would be if North Korea was willing to fulfil promises made in a joint statement in September 2005, when the country agreed to abandon its nuclear programme in exchange for aid and pledges from the US that it would not seek to destabilise the North Korean government.
In Washington, Mark Toner, the US State Department's spokesman, said that the US was "cautiously optimistic" about Thursday's talks.
Toner said food assistance would be discussed in the talks, but that the United States has some concerns it wants North Korea to address. He did not say what those concerns were, but analysts have said North Korea must agree to have UN watchdogs monitor any freeze of its uranium enrichment.
Davies, who is accompanied by Clifford Hart - the US special envoy for the six-party talks - will also meet his Wu Dawei, his Chinese counterpart, on his trip to China, before leaving on Saturday for South Korea.
Key nuclear summit
Worries about North Korea's nuclear capability took on renewed urgency in November 2010 when the country disclosed a uranium enrichment facility that could give it a second route to manufacture nuclear weapons, in addition to its existing plutonium-based programme.
As the envoys began talks in Beijing, North Korean state media criticised next month's Nuclear Security Summit, to be held in Seoul.
"It is illogical to discuss the 'nuclear security' issue in South Korea, the US nuclear advance base and a hotbed of nuclear war," the North's official Korean Central News Agency said in a commentary Thursday.
The North said it is "worse still" to hold the summit during joint US-South Korean military drills scheduled for the next few months, which the commentary called "rehearsals for a nuclear war against the North".
Seoul and Washington say the annual drills are defensive in nature.