Pics shown of young North Korean leader

North Korean leader Kim Jong Un holds up parliament membership certificate during the Supreme People's Assembly in Pyongyang. Photo / AP

Photographs of Kim Jong-un as a boy have emerged during a concert for the North Korean air force.

Pictures showing the 31-year-old North Korean leader as a chubby toddler, saluting while in uniform, were shown on KCTV, the country's state broadcaster.

Until now, only a handful of pictures of Kim as a boy have been seen, one showing him with his mother, Ko Yong-hui, and one a seeming passport picture, in which he has a bowl haircut.

Only one photograph is known to exist from his days as a student, which shows him on what appears to be a school trip with fellow pupils at the International School of Berne in Switzerland. His identity was kept secret from students and teachers.

Kim Jong-Un at the first meeting of "airpersons" of the Korean People's Army in Pyongyang. Photo / AFP

The new pictures were projected on to a screen behind an orchestra playing a televised concert for the air force.

As the photographs emerged, South Korea warned that the North could be planning a fourth nuclear test to ramp up tensions ahead of President Obama's forthcoming visit to Seoul.

"Our military is currently detecting a lot of activity in and around the Punggye-ri nuclear test site,'' said Kim Min-seok, a spokesman for the defence ministry. He added that North Korea is able to conduct a nuclear test "at any moment''.

A picture of North Korean leader Kim Jong-un is sprayed by a protester in Seoul, South Korea. Photo / AP

Barack Obama is visiting Seoul as part of an Asia tour, and it has been speculated that the North may stage a provocation to coincide with the trip.

Early this week, Pyongyang criticised Mr Obama's trip as a "dangerous'' move.