North Korean leader Kim Jong-un made no mention of friendship in a congratulatory message to China marking its National Day on Wednesday. The omission hints at how badly ties between the allies have deteriorated.

In the three-paragraph message to Chinese President Xi Jinping, Kim expressed good wishes for China's future prosperity and the happiness of the Chinese people, according to the North's official Korean Central News Agency. But there was no mention of the special relationship between the two countries.

Last year, Kim still underscored the strength of the alliance, which was forged on the battlefield in the 1950-53 Korean War.

Pundits say the omission was probably payback for China's omission of the traditional formula for bilateral ties in a congratulatory message for the North's founding day on Sept. 9.

Until the end of Hu Jintao's presiden cy, Beijing always referred to "tradition, future relationship, friendship, and cooperation" between the two sides in its congratulatory messages to Pyongyang.

But once Xi came into office, the formula was omitted.

Kim Heung-kyu at Ajou University said, "What we are seeing is a tit-for-tat diplomacy in which neither side can afford to back down."