North Korean leader Kim Jong-un's younger sister, who was believed to be pregnant, made her first public appearance in about 50 days, the North's media reported Friday, cementing speculation that she might have given birth in May.

Kim Yo-jong, 28, accompanied the young leader on his field guidance to a tree nursery, which is being constructed by the Korean People's Army (KPA), according to the North's Korean Central News Agency (KCNA).

In April, South Korea's spy agency said that Kim would likely give birth in May, adding that her husband may be an alumnus of her alma mater, Kim Il-sung University. The agency did not provide more details.

Kim Yo-jong made her last public appearance April 12 when she accompanied the current leader on his inspection to the construction site of a second airport terminal in Pyongyang.

Experts said that her absence seemed to back up speculation that she has recently given birth.

In November last year, North Korea unveiled her official title: deputy director of the North's ruling Workers' Party of Korea.

Both the current leader and his sister were born to Ko Yong-hui, known as the fourth wife of late leader Kim Jong-il. (Yonhap)