SEOUL -- North Korea's political leaders recently sent a series of congratulatory message to China's newleadership, state media have reported, amid rumors of diplomatic dispute between the close allies over the North's third nuclear test.

The North's Premier Choe Yong-rim sent a message on Saturday to Li Keqiang to congratulate him on his election as China's new premier, according to the North's official Korean Central News Agency (KCNA).

Choe, in the message, "expressed hope that the Chinese people will have great success in their struggle to attain sustainable and fast growth of economy and improve their national power and that the traditional friendly and cooperative ties between the two countries will be furthered through joint efforts by both sides," the KCNA said in a Korean-language dispatch.

Foreign Minister Pak Ui-chun sent a congratulatory message to his new Chinese counterpart Wang Yi on the same day.

On Thursday, North Korean leader Kim Jong-un and the country's ceremonial head of state Kim Yong-nam sent messages congratulating Xi Jinping and Zhang Dejiang on their elections as China's president and top legislator, respectively.

This marks the first time that the Pyongyang leadership has sent any message to Beijing since North Korea's test-firing of a long-range rocket late last year triggered rumors of diplomatic dispute between the two countries.

Speculations are that North Korea complained to China because the communist ally joined the U.N. Security Council's adoption of new sanctions against Pyongyang's Feb. 12 nuclear test.

Kim Jong-un did not reply to Xi's New Year's greeting card and Pyongyang's state media failed to report on political news from China for the past several months.

Experts say the resumption of North Korea's "letter exchanges" with Chinese leaders is seen as a groundwork for ending the discord between the two allies timed with the launch of the new Chinese leadership and preparations for Kim's possible visit to China. (Yonhap News)