North Korea envoy meets Chinese President Xi Jinping

Choe Ryong-hae has met numerous senior Chinese Communist party officials

A North Korean envoy visiting China has met President Xi Jinping and handed him a letter written by Kim Jong-un, Chinese state media has reported.

The letter was handed over by the envoy, Vice Marshal Choe Ryong-hae.

The contents of the letter were not disclosed, but North Korea said earlier that it was willing to take "positive action" to improve strained relations.

They cooled after China supported tightened UN sanctions following North Korea's third nuclear test in February.

Vice Marshal Choe has said that his country was willing to make joint efforts to resolve problems through six-party talks and other forms of dialogue, the state-run China News Service said.

China is North Korea's biggest trading partner and closest ally.

Earlier Vice Marshal Choe met senior Chinese official Liu Yunshan, a member of the Standing Committee of China's Political Bureau.

He is the most senior North Korean official to visit China since August 2012 and the talks follow weeks of tension on the Korean peninsula and a series of threats from the North.

Mr Liu said that all relevant parties should support the goal of denuclearisation, and also called for a return to six-party talks, Chinese media said.

Vice Marshal Choe said North Korea appreciated China's efforts to maintain peace and stability, and was "willing to accept the suggestion of the Chinese side and launch dialogue with all relevant parties", China's state-run news agency Xinhua reported.

Traditional allies

In recent months Beijing has increasingly voiced frustration with Pyongyang's actions

The two neighbours generally enjoy warm relations.

China has prioritised maintaining stability in North Korea to avoid any crisis that could trigger the fall of the regime and propel a flow of refugees across the border.

But following North Korea's third nuclear test, China adopted a tougher stance.

It supported tightened UN sanctions, and some of its banks have recently suspended trading with North Korea's Foreign Trade Bank.

Relations were also strained after a Chinese fishing boat, with 16 crew members, was seized in the Yellow Sea by unidentified North Koreans.

The crew were released two weeks later.

Tensions in the Korean Peninsula were heightened earlier this year, as Pyongyang threatened to restart a mothballed nuclear reactor and increased its rhetoric with threats to attack Japanese, South Korean and US military targets in the region.