Kim Jong-un, right, has been appointed supreme commander of the military and ruling party leader [Reuters]

South Korea's president has opened the door to possible nuclear talks with North Korea, but pledged to respond strongly to any provocations from Pyongyang.

President Lee Myung-bak said on Monday in a nationally televised speech that the Korean peninsula was at a "turning point".

The comments came as the young son of the late Kim Jong-il took power in North Korea as supreme commander of the military and ruling party leader after Kim's death last month.

The North announced on Sunday in a New Year's message that it would bolster its military and defend the son, Kim Jong-un, "unto death".

"The situation on the Korean peninsula is now entering a new turning point," Lee said. "But there should be a new opportunity amid changes and uncertainty."

He said that if North Korea demonstrated sincerity, a new era on the Korean peninsula could be opened, but said that South Korea would sternly respond to any attack from Pyongyang.

North Korea has regularly criticised Lee since he took office in 2008 and ended a no-strings-attached aid policy towards the North. Lee has sought to link aid to progress in North Korea's nuclear disarmament.

In his speech, Lee reasserted that if North Korea halted its continuing nuclear activities there could be a resumption of international disarmament-for-aid negotiations meant to rid the North of its nuclear programmes.

A sincere attitude from North Korea could lead to better relations between the rivals, he said.

Precondition missing

Cross-border ties have been icy since the South accused the North of torpedoing one of its warships in March 2010 with the loss of at least 46 lives.

The North denied involvement but killed four South Koreans in an artillery attack on a border island in November 2010.

Al Jazeera's Harry Fawcett, reporting from Seoul, noted the omission of a previous precondition of an apology or acknowledgement from the North for the deaths of the people in the attack on the warship and the artillery deaths on Yeonpyeong island.

Speaking to Al Jazeera, John Park, a Korean affairs expert and research fellow at Harvard's Belfer Centre for Science and International Affairs, said Lee was trying to seize the higher ground, but that North Korea was already taking a very strong line against South Korea.

Pyongyang said on Friday that there would be no softening of its position towards South Korea's government after Kim Jong-il's death.

North Korea's powerful National Defence Commission said the country would never deal with Lee.

Fawcett said: "Everything the North Korea is doing at the moment is designed to project stability and continued power and strength.

"Any movement toward anything which might be interpreted as a weakness will be avoided."

He said the question was whether North Korea felt it was in a secure enough position to respond to South Korea's overture and whether Kim Jong-un wanted to.