South Korea has dismissed North Korean leader Kim Jong Un's calls for improved ties, urging his government to take nuclear disarmament steps first.



Kim Eui-do, South Korean Unification Ministry spokesman, told reporters on Friday that North Korea should first make "sincere" efforts for nuclear disarmament, if it wanted to improve strained ties with Seoul.



"In order to improve ties between the South and the North, North Korea must show sincerity in building trust and above all, it must make genuine efforts for denuclearisation," the ministry spokesman said in a statement.



The North Korean leader made the overture in a New Year's Day speech on Wednesday that included typical rhetoric against Seoul and Washington and a warning of a possible nuclear war.



But he also called for a "favourable climate" to improve relations with the South, saying it was time for the two Koreas to stop doing "anything detrimental to national unity and reconciliation".

In response,Seoul said it was doubtful about Pyongyang's assertion because the country made a similar offer in a New Years' Day message last year but quickly followed that with a nuclear test and a string of military threats that sharply raised tension on the peninsula.



Analysts said North Korean leader Kim's hopes for better ties with South Korea could be linked to his vow to revive the country's economy and improve his people's living standards.



Prospects for inter-Korean relations were put in doubt after last month's execution of Kim's once-powerful uncle and mentor Jang Song Thaek on treason charges in the biggest political upheaval since Kim took power following the death of his father Kim Jong Il in late 2011.



Seoul officials have said North Korea may increase provocations against South Korea to bolster internal unity to cope with possible instability triggered by Jang's execution.



In his New Year's Day speech, Kim said the country's unity has been strengthened after the elimination of "factionalist filth" in a reference to his late uncle.