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

Mr. Kim made the overture in his New Year’s Day speech on Wednesday that also included typical rhetoric against Seoul and Washington and a warning of a possible nuclear war.

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

Analysts said North Korean leader Mr. Kim’s hopes for better ties with South Korea could be linked to his vow to revive the moribund economy and improve his people’s living standards as outside investment and aid are necessary to realize his promise.

Prospects for inter-Korean relations were put in doubt after last month’s execution of Mr. Kim’s once-powerful uncle and mentor Jang Song Thaek on treason charges in the biggest political upheaval since Mr. 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, Mr. Kim said the country’s unity has been strengthened after the elimination of “factionalist filth” in a reference to his late uncle.

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