North Korea and the US say they have had positive talks over Pyongyang's nuclear weapons programme.
Christopher Hill is preparing the ground for more six-party talks
But the US denied reports from the North that an agreement was reached when chief negotiators for the two sides met in Berlin this week.
US envoy Christopher Hill has arrived in South Korea to prepare the ground for the next round of six-party talks.
He told reporters he hoped they would begin before the Lunar New Holiday, which starts in mid-February.
The talks ended inconclusively in December, having resumed after a break of more than a year.
Mr Hill and his North Korean counterpart, Kim Kye-gwan, ended three days of unprecedented talks on Thursday.
Talks in December made no real breakthrough
The Berlin meeting took place "in a positive and sincere atmosphere, and a certain agreement was reached there", a spokesman for the North was quoted as telling state news agency KCNA.
Mr Hill called the talks "very useful" but, when asked about North Korea's talk of an agreement, appeared puzzled, telling reporters: "I'm sorry, I'm not really sure what he's referring to."
The BBC correspondent in Seoul, Charles Scanlon, says the North's statement is unusually positive.
He says the North is clearly encouraged by signs of growing flexibility in Washington's position, just four months after it tested its first nuclear device.
For years the US rejected demands for direct bilateral talks, but this week Mr Hill was allowed by his government to sit down for discussions with Mr Kim.
The US is also holding direct talks with the North on the financial sanctions it imposed in 2005, which it said at the time was a question of law enforcement and was non-negotiable.
These sanctions prompted the North to walk away from the negotiations for more than a year.
But while Pyongyang may see the talks as "direct dialogue held by the [North] and the US", Washington views the situation rather differently.
"This is not an instance of bilateral negotiations," White House spokesman Tony Snow told Reuters news agency.
"What you had ...this week in Berlin were talks with Chris Hill and a North Korean representative as preparations for the six-party talks".
Mr Hill echoed that view, saying that while discussions between rounds of talks were useful, "the negotiations for the denuclearisation of the Korean peninsula take place at the six-party talks".
From Seoul, Mr Hill will travel to Beijing and Tokyo to prepare the ground for the new round of talks, which bring together North and South Korea, China, Japan, Russia and the US, and are aimed at persuading Pyongyang to scrap its nuclear ambitions.