North Korean leader Kim Jong Un said it was time for the two Koreas to stop doing "anything detrimental to national unity and reconciliation," while also warning of a possible nuclear war. KCNA/Reuters

South Korea on Friday dismissed North Korean leader Kim Jong Un's calls for a more "favorable climate" on the peninsula, urging his government to first take steps toward nuclear disarmament.

Kim Eui-do, South Korean Unification Ministry spokesman, told reporters that North Korea should make "sincere" efforts toward that goal if it wants to improve relations 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 denuclearization," a statement from the ministry spokesman read.

The North Korean leader made the overture in a speech on Wednesday that also included typical rhetoric directed against Seoul and Washington — and a warning of a possible nuclear war.

But he also called for a "favorable 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 skeptical of Pyongyang's assertion because the country had made a similar offer in a New Year's Day message last year but quickly followed that with a nuclear test and a string of military threats.

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 — 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 the South to bolster internal unity to cope with possible instability triggered by Jang's execution.

In his speech this week, Kim said the country's unity has been strengthened after the elimination of "factionalist filth," a reference to the uncle he had executed.

Al Jazeera with wire services