 Christopher Hill said he had come in the spirit of making real progress |
It is the first time the two have held bilateral talks ahead of the six-party process.
But before meeting Kim Kye-gwan, US negotiator Christopher Hill stressed they were not holding private talks.
BBC correspondent Charles Scanlon in Seoul says few are expecting a breakthrough at this meeting.
However, he adds, negotiators say this time they will be more flexible and will discuss the problems in more detail.
'Measurable progress'
The main six-nation talks - involving delegates from North and South Korea, China, Japan, Russia and the US - are due to begin on Tuesday in the Chinese capital, Beijing.
Mr Hill said over the weekend that he had come to the talks in the spirit of making real progress.
North Korea agreed to resume the six-nation talks earlier this month, more than a year after it suspended them, blaming US aggression.
Washington's aim in the talks - now in their fourth round - is to persuade North Korea to stop developing nuclear weapons in return for economic aid and security guarantees.
 N Korea blamed US aggression for the suspension of talks |
"We're just trying to get acquainted... and compare notes," Mr Hill told reporters.
"I wouldn't expect this to be the last set of negotiations... we would like to make some measurable progress, progress we can build on for a subsequent round of negotiations."
"We come here in a real spirit of trying to make some real progress."
South Korean Deputy Foreign Minister Song Min-soon echoed the comments after meeting his northern counterpart.
"We shared the view that participants in the talks should produce substantial progress and come up with a framework for the realisation of a nuclear-free Korean peninsula," Yonhap news agency quoted him as saying.
Pyongyang has been making calls for a peace treaty with the US in the days leading up to the talks.
But Washington has been refusing to talk about any kind of pact until North Korea agrees to shut down its nuclear weapons programme.
The US has indicated that the country could face further sanctions if it fails to resolve the nuclear crisis, although it has stressed that it does not intend to attack the North.
