Seoul, June 15 : North Korean leader Kim Jong-un has sent a letter to Chinese President Xi Jinping on the latter's 70th birthday, saying that Beijing's national power has "remarkably" strengthened under his leadership, Pyongyang's state media reported on Thursday. In the message, Kim said that Beijing has "built a comprehensively well-off society" and that its "national power and international position remarkably strengthened" under Xi's "energetic" leadership, according to North's official Korean Central News Agency (KCNA). "The message expressed belief that the struggle for the prosperity of China will surely emerge victorious as there are the leadership of Xi Jinping and the Chinese party and people rallied around the Party Central Committee with him as its core," Yonhap News Agency quoted the KCNA as saying. Kim also said he is pleased to see Xi's achievements and wished him more success in his "important and responsible work" in leading China. The North Korean leader sent a flower basket to Xi, which the North Korean ambassador to China delivered to the deputy head of the International Liaison Department of the Chinese Communist Party on Tuesday, according to the KCNA. The message came as the North has been seeking to strengthen ties with China, its traditional ally and economic benefactor, amid global sanctions on its nuclear and missile programs, and stalled denuclearisation talks with the US. Last October, Kim also sent a letter to Russian President Vladimir Putin on his 70th birthday, lauding his leadership and expressing hope for bilateral ties between their countries to further develop. /IANS