The communist North has heaped insults on the conservative leader since he took office in February and pledged a firmer line in cross-border ties. It has cut off official contacts with the South.
Lee, in an interview with Kyodo News published yesterday, said he is always ready to meet the North's leader Kim Jong-Il "as many times as I can" for genuine dialogue to improve relations.
But the North's state Committee for the Peaceful Reunification of the Fatherland rejected the idea.
A committee spokesman quoted by the official Korean Central News Agency said it is "preposterous" for Lee to make such a suggestion when he ignored "important declarations" at previous summits.
Lee's liberal predecessors held summits in Pyongyang in 2000 and 2007 which eased relations. Lee has said he will study joint economic projects agreed in 2007 before giving them the go-ahead.
"It is absolutely intolerable to overturn the north-south declarations on account of the change of power as it is rude behaviour betraying the lack of any elementary morality and a blatant act of chilling the desire of the whole nation," the spokesman told the official news agency.
