China's ruling Communist Party has yet to receive an invitation from North Korea to attend a rare party congress in May, a diplomatic source with knowledge of the matter said Monday. 

North Korea is gearing up to hold the Workers' Party Congress in May. The last such party conference was held in 1980 and China sent a vice premier to Pyongyang at that time. 

"To my knowledge, China and other communist nations such as Vietnam and Cuba, have not received an invitation from North Korea for the party congress in May," the source said on the condition of anonymity. 

North Korea conducted its fourth nuclear test on Jan. 6 and launched a long-range rocket about a month later, prompting the U.N. Security Council to tighten sanctions against the North.  

China, North Korea's diplomatic and economic lifeline, backed the new U.N. sanctions. 

During the May party congress, North Korea's young leader Kim Jong-un is expected to unveil new policies on issues ranging from the economy to relations with South Korea. (Yonhap)