N. Korea Sends China Communist Party Faint Praise

North Korea issued an unusually short congratulatory message to China's Communist Party Wednesday as President Xi Jinping opened its five-year congress amid strained ties between the two traditional allies.

China is North Korea's longtime ally and economic benefactor, saving the country from defeat during the 1950-53 Korean War.

But the relationship has soured in recent months over Pyongyang's growing weapons ambitions, which have seen Beijing agree to toughened United Nations sanctions.

In a three-paragraph message carried by the official KCNA news agency, the North's ruling Workers' Party of Korea (WPK) "warmly congratulated the 19th Congress of the Communist Party of China and sent warm greetings to all the party members and other Chinese people".

"The Chinese people have made great progress in accomplishing the cause of building socialism... and we are greatly pleased over this," it added.

But the statement made no mention of the historic ties between Beijing and Pyongyang, in contrast to the one issued for the last Chinese Communist congress in 2012, when outgoing leader Hu Jintao was praised by name.

It referred to "the fraternal Chinese people" and, using the acronym for the North's official name, said the Workers Party would "protect the traditional DPRK-China friendship provided and cultivated by the elder generation of the two parties and countries and invariably develop it generation after generation".

The relationship between Beijing and Pyongyang was forged in the blood of the Korean War, when Mao Zedong sent millions of "volunteers" to fight US-led United Nations forces to a standstill.

Mao described the allies as close as "lips and teeth", and China has long been accused of failing to enforce sanctions even after voting for them at the UN.

While Beijing's official goal is to bring Pyongyang back to the negotiating table to curb its nuclear ambitions, it has grown increasingly frustrated by its belligerent neighbour.

After a flurry of missile launches by the North and its sixth nuclear test last month, China backed new UN sanctions that included bans on imports of coal, iron ore and seafood from the North, as well as limits on exports of oil products to it.

But analysts say there still appears to be scope for the fractured relationship to improve.

"The fact that North Korea sent a congratulatory message signals that the relationship is not at its lowest point," said Kim Han-Kwon, a professor at the Korea National Diplomatic Academy.

China will not easily abandon North Korea, Kim said, which serves as a buffer state against the United States.

"From the outside China will bolster sanctions against the North, but it will not risk actions that will devastate the leadership in Pyongyang," he said.