Kim Jong Un remembered his late father as he toured North Korean locomotive factories on Sunday. REUTERS

Kim Jong Un publicly expressed grief over his father's death -- a rarity for the young North Korean leader -- in remarks Sunday, as he toured a train manufacturing facility in the country's capital, Pyongyang.

While at the locomotive factory, he lamented the death of the elder Kim, who had reportedly died of a heart attack in 2011 while on a moving train for an official business trip. "If only we had a better rail system, my heart would not be in such pain," Kim said, according to South Korean outlet No Cut News.

He also attributed North Korea's modernization to his father, who boarded the trains "day and night."

"Every now and then, as I tour the facilities, I think of the great, difficult guidance the People's Leader [Kim II Sung] and the General [Kim Jong II] provided, in their lifelong dedication to people and fatherland," Kim said according to North Korea's KCNA. South Korea media acknowledged these remarks as a "rare expression of longing for his late father," reported United Press International news agency.

Kim visited the Kim Jong Thae Electric Locomotive Complex to provide field guidance and suggestions for modernization. While there, Kim gave instructions for producing more electric locomotives that use the "latest technology."

Sunday's remarks came after the end of the customary three-year mourning period for a parent, which was commemorated in December with a ceremony held at Kumusan Palace of the Sun in Pyongyang, where Kim Jong Il’s body lies.

Trains, ships and cars blared their horns as North Koreans participated in a three-minute silence at noon to mark the anniversary of his death, reported the Los Angeles Times. With this period passed, Kim now has the ability to make policies that reflect his own ideology, as opposed to those instated by his father.