The US team was the first from the outside world to be allowed into North Korea's Yongbyon complex since UN inspectors were expelled a year ago.
Two members of the unofficial US delegation, Keith Luse and Frank Jannuzi, both Senate foreign relations committee aides, flew into Seoul on Sunday, but they declined to discuss their visit to Yongbyon.
They met officials from South Korea's unification ministry and briefed them on their five-day visit to North Korea.
"We look forward to fulsome discussions with your government about our recent trip to North Korea and we look forward to the close coordination between our two governments in the peaceful resolution of the North Korean nuclear problem," Jannuzi told Park Chan-bong, a senior unification ministry official.
The two Senate aides were scheduled to meet foreign ministry officials on Monday evening.
John Lewis, a professor emeritus at Stanford University, had led the delegation to North Korea.
Pyongyang said on Saturday it had shown a visiting US delegation its "nuclear deterrent" and hoped it would provide a basis for a peaceful settlement of the row with the United States over its nuclear activities.
Powell said the US was committed
to the next round of talks
The US suspects North Korea may have resumed reprocessing spent nuclear fuel rods into plutonium for use in nuclear weapons and has been trying to resume six-way talks to end the nuclear row.
The six parties - the two Koreas, the US, China, Japan and Russia - met inconclusively in Beijing in August.
Japan's Nihon Keizai Shimbun quoted State Councillor Tang Jiaxuan as saying he expected the next round of six-party talks to be held in February.
Tang, a former Chinese foreign minister, told a delegation of Japanese officials the talks looked likely next month because North Korea and the US appeared to be getting closer to overcoming their differences.
Meanwhile, the state media in North Korea marked the first anniversary of the country's pull-out from the Nuclear Non-proliferation Treaty with a commentary on Sunday blaming the US for ignoring Pyongyang's overtures for a resolution of the crisis.
"The world is now watching whether the US has a true will to settle the nuclear issue on the Korean peninsula on the principle of simultaneous actions and peaceful co-existence," the North's mouthpiece, news agency KCNA, reported on Sunday.
US Secretary of State Colin Powell told Japan's NHK television on Sunday Washington was committed to the next round of talks and he was confident it would be held in the "not-too-far future".
Last week, North Korea offered to freeze its nuclear activities in a move that has raised hopes for a fresh round of talks.
The US said in October 2002 that North Korea had admitted to a clandestine uranium enrichment programme to build nuclear weapons, which US officials say violated a 1994 agreement by the North to freeze its nuclear programme.