Roh Moo-hyun also said in a speech to the National Assembly that the reclusive communist state's test of a nuclear device on October 9 had undermined peace on the Korean peninsula.
"North Korea's nuclear test was a foolish act indeed," Roh said in remarks delivered to parliament by the prime minister.
"The nuclear arsenal will only jeopardise the stability of the North Korean regime and bring about severe economic difficulties," he said.
Last week, North Korea said it would return to stalled six-country talks on ending its nuclear weapons programme.
South Korean and US officials said they expect the next round of the talks among the two Koreas, China, Japan, Russia and the United States to be held in November or December.
Roh said South Korea would abide by UN sanctions on North Korea put in place after the test but that Seoul would not pull the plug on two major projects it has in the North -- a mountain resort and an industrial park -- that have been criticised for providing the North's leaders with cash.
Roh said he did not think the road for the six-way talks would be smooth.
North Korea has already clouded the picture by saying Japan should not get a seat at the table and placing high emphasis on using the discussions to end a US crackdown on its international finances.
"It will require diverse procedures and take a long time before the nuclear issue is resolved completely," Roh said.

Copyright Reuters, 2006