Pyongyang's official Korean Central News Agency (KCNA) said in the report that Ri was elected during a four-day plenary meeting of the party's eighth Central Committee that concluded on Thursday. 

Meanwhile, Kim Song Nam, another party official, was also named an alternate member of the politburo, while O Su Yong was elected as director of the party's Department of Economic Affairs, Xinhua news agency quoted the KCNA report as saying. 

North Korea held the plenary Central Committee meeting to discuss how to implement the first year's tasks of a five-year economic development plan set forth during last month's eighth party congress. 

The country's leader Kim Jong-un watched a Lunar New Year performance on Thursday together with members of the party central leadership organ after the multi-day plenary meeting, the KCNA report added.