Japan's NHK says that the eldest son of North Korean leader Kim Jong-il has returned to Pyongyang from a long stay abroad and is working for the North Korean Worker's Party.

The Japanese public broadcaster quoted a South Korean intelligence official as saying that Kim Jong-nam returned to North Korea in June, and is working for the party-affiliated Organization and Guidance Department. The junior Kim had worked there when he was considered a promising successor to his father after graduating from college.

But NHK also said that it remains to be seen whether he could inherit the reins from his father over his younger half-brothers.

Kim Jong-nam had lived in exile in Macao until recently due to alleged conflict with his father.