South Korea on Thursday urged North Korea to match its emollient rhetoric with actual deeds after the communist state's leader Kim Jong-Il offered nuclear concessions during his visit to Russia.

"I don't see any particular progress," Deputy Spokesman Shin Maeng-Ho of the South's foreign ministry told AFP.

At rare talks in Russia, Kim on Wednesday promised Russian President Dmitry Medvedev that his reclusive state was prepared to renounce nuclear testing and processing if long-stalled discussions resume.

The nuclear-armed North stormed out of six-party negotiations -- which bring together the two Koreas, China, the US, Russia and Japan -- in April 2009 and conducted its second nuclear test a month later.

Shin told journalists that Kim's reported statement is ambiguous about what the North will do about its nuclear activities before or after the talks resume.

He added that South Korea's chief envoy to the six-party talks, Wi Sung-Lac, left for Beijing Thursday for discussions with his Chinese counterpart Wu Dawei.

According to a Russian regional official, the North Korean leader will head to China himself following the completion of the discussions in Siberia, although it was not clear whether he would stop in the country or head home.

The JoongAng Ilbo newspaper quoted an unidentified government official as saying that Seoul wanted the six-party talks to resume at an early date.

"But the key is whether the North takes actions for denuclearisation before the talks resume. In that sense, the recent announcement fails to show North Korea's sincerity in purpose," the official told the daily.

The South demands that the North allow inspectors back to monitor its nuclear sites, stop nuclear processing activities and suspend testing of weapons of mass destruction before the six-party talks resume.

"Without preconditions, in the course of the negotiations" the North will be ready to introduce a moratorium on testing and spent nuclear fuel processing, Kremlin spokeswoman Natalya Timakova said.

Analysts said the Kim-Medvedev talks had helped sweeten the atmosphere for the resumption of the six-party talks, which have been at a standstill since the last meeting in December 2008, but both sides have a long way to go.

Last November Pyongyang disclosed an apparently functional uranium enrichment plant, which can provide it with a second way to make material for atomic bombs in addition to its plutonium stockpile.

"The key issue is the uranium enrichment programme and it will take a lot more time for the North and the United States to narrow differences," Professor Yang Moo-Jin of the University of North Korean Studies told AFP.

Russia is not as close to North Korea as its key ally China, but Medvedev told journalists that Pyongyang supported a planned pipeline to carry Russian gas supplies to energy-hungry South Korea through the North, a route that would allow Moscow to reach new Asian markets.

Shin, of Seoul's foreign ministry, admitted the progress of the project would be influenced by the nuclear issue as well as inter-Korean relations.

"We have to wait and see the progress in Russo-North Korean discussions on this issue. We also have to take inter-Korean ties into account. The North's nuclear issue will also affect it," Shin told AFP.