"The possibility of North Korea pushing ahead with a nuclear test before the (85th) anniversary of the founding of the Korean People's Army on April 25 cannot be ruled out," Cheong said in a forum in Seoul.

"It is assumed that North Korea would finish sophisticating its nuclear capabilities through the last nuclear test ahead of the launch of a new administration in the South before seeking to mend the fence with the new administration using a nuclear test freeze as a negotiating card," he noted.

South Korean officials believe North Korea is ready to conduct its sixth nuclear test at any time upon its leader's decision.

Since 2006, North Korea has carried out a total of five nuclear tests. Experts said the country may be just a few tests away from achieving a complete nuclear weapon system.

On May 9, South Korea will hold an early election to pick a president who will succeed Park Geun-hye after her ouster in March over a massive corruption scandal.

Cheong said North Korea may launch a satellite rocket first and then attempt a nuclear test or an intercontinental ballistic missile launch in protest of likely international sanctions and condemnation on the satellite launch. (Yonhap)