North Korea is marking the 112th birthday of its late leader Kim Il Sung on Monday amid concerns it may use the occasion to launch another spy satellite.

North Korea's founder was the grandfather of current leader Kim Jong Un, and April 15 is one of the most important national holidays. A mass ceremony was held on Sunday in the capital Pyongyang.

The country's ruling Workers' Party newspaper, Rodong Sinmun, called on people to devote all their wisdom and passion to the party.

Pyongyang had previously said it plans to put three more military reconnaissance satellites into orbit this year.

South Korea's Defense Minister Shin Won-sik told public broadcaster KBS on Sunday that the satellite launch has apparently been delayed.

He said North Korea has been preparing for a launch on April 15 but it seems to have been postponed for technical reasons.

Shin said that Pyongyang could carry out the launch in a few days or by the end of the month at the latest.