The third son of North Korean leader Kim Jong Il has been assigned to the country's all-powerful National Defense Commission, a possible sign that he is being groomed as his father's successor, a news report said Sunday.

Kim, who has ruled the nuclear-armed North with absolute authority since his father's death in 1994, has three known sons by two women but has not publicly anointed any of them as his successor. Speculation on who is to succeed the 67-year-old leader has grown since Kim reportedly suffered a stroke in August.

On Sunday, Yonhap news agency reported Kim's youngest son, 26-year-old Kim Jong Un, took up a low-level post at the defense commission, several days before the country's rubber-stamp parliament reappointed the senior Kim as the commission's chairman on April 9.

Under the North's Constitution, the defense commission is the top government body and Kim Jong Il has ruled the country in his capacity as its chairman. He also is the top official in the powerful Workers' Party and supreme commander of the army.

At this month's closely watched parliamentary session, Kim Jong Il looked thinner and grayer and was limping slightly. It was Kim's first major public appearance since his reported stroke but proved that he remains in charge of the communist North.

Yonhap, citing unidentified sources it says are privy to North Korea affairs, reported the third son is expected to assume the defense commission's higher-level posts step by step in preparation to succeed his father.

The National Intelligence Service — South Korea's main spy agency — said it was aware of the Yonhap report but could not confirm it. The Unification Ministry was not immediately available for comments on the report.

Little is known about Kim Jong Un except that he studied at the International School of Berne in Switzerland. Kim Jong Il's former sushi chef says in a 2003 memoir that the son looks and acts just like his father and is the leader's favorite.

Tension on the Korean peninsula is running high on the Korean peninsula following the North's defiant rocket launch on April 5. The U.N. imposed new sanctions on three North Korean companies over the launch that many believe was a test of the North's long-range missile technology. In response, the North said Saturday it has reactivated its nuclear facilities to harvest plutonium for atomic weapons.