South Korea's Yonhap news agency said the North's leader Kim Jong-Il has promised not to stage a second nuclear test unless it is "harassed" by the United States.
The report quoted diplomatic sources in Seoul as saying Kim gave the assurance during a meeting in Pyongyang last week with a high-level Chinese delegation led by State Councillor Tang Jiaxuan.
"Kim said during a meeting with Tang that North Korea would not conduct an additional nuclear test unless the US harasses the North," Yonhap quoted one source as saying.
"Kim also promised North Korea would return to the six-way (disarmament) talks in the near future as long as the US promises to lift financial sanctions after the talks reopen."
South Korean officials said they had no information on the report. Yonhap on Friday quoted a diplomatic source in Beijing as saying Kim had told his Chinese visitors there would be no additional test.
Tang was the first foreign official to meet Kim since North Korea sparked world outrage and UN sanctions with its first atomic test on October 9.
After his return to Beijing Tang Friday said his trip had not been a waste of time but gave no details.
"Fortunately my visit this time has not been in vain," he told visiting US Secretary of State Condoleezza Rice.
Chinese Foreign Minister Li Zhaoxing also reported some positive elements from the meeting, saying the prospect of quickly resuming stalled six-party talks on the North's nuclear program had been discussed.
North Korea agreed at the talks in September 2005 to scrap its nuclear programmes in exchange for energy aid, other economic inducements and security guarantees.
But it boycotted the forum two months later in protest at US attempts to
cut its access to overseas banks.
Japanese Foreign Minister Taro Aso was also quoted as saying Friday his country has information that Kim promised Tang there would not be another test. And a South Korean newspaper said Kim had expressed regret to the envoy from China, the North's most crucial source of aid and trade.
In Moscow, Rice cast doubt Saturday on the reported apology and said the North wants an "escalation of tensions."
"I don't know whether or not Kim Jong-Il said any such thing," Rice said.
"But the Chinese, in a fairly thorough briefing about the talks, said nothing about such an apology for having launched a test," she added.
Rice was headed home Sunday after a tour of the North's neighbours aimed at securing support for tough enforcement of the UN sanctions, and US officials said she seemed to have been successful.
Rice visited Japan, South Korea and China before Moscow.
"It seems clear that the Russians take (sanctions resolution) 1718 seriously," a senior State Department official said. "They talked about tightening some of their controls on the border."
Russia and China, traditional allies of Pyongyang and normally opponents of sanctions as a diplomatic weapon, both negotiated in the UN Security Council to scale back tougher restrictions pushed by the United States and Japan.
The biggest surprise may have been in Beijing, where one of Rice's top aides said there had been a "sea change" in China's attitude since the test.
A key stumbling block has concerned inspections of North Korean cargo shipments, which are provided for under the UN resolution but which have been resisted by China and South Korea for fear of aggravating tensions.
Japan is ready to go ahead, according to a media report.
It plans to inspect cargo to and from North Korea in two sea-lanes close to its territory, the Yomiuri Shimbun said.
The paper said the government is considering deploying several destroyers and P-3C patrol aircraft to the Tsushima Strait and to waters close to the southernmost islets of Okinawa.
The United States says it wants to prevent the North from transferring weapons of mass destruction and nuclear know-how to groups and governments hostile to the United States.
Both Japan and South Korea are under the US nuclear defence umbrella, and Rice also used her visits to underline US commitments to defend them in the event of a North Korean attack.
Her trip coincided with annual military talks between the United States and South Korea in Washington, where US Defense Secretary Donald Rumsfeld met his South Korean counterpart Yoon Kwang-Ung.
The language of their joint statement after the talks was somewhat tougher than in previous years, promising Seoul "assurances of firm US commitment" against attack.

Copyright AFP (Agence France-Presse), 2006