BEIJING (Reuters) - The Chinese government has appointed a new ambassador to North Korea, an important and sensitive diplomatic post at the centre of efforts to get the reclusive country to end its nuclear weapons ambitions.

Mr Li Jinjun is replacing Mr Liu Hongcai in the position, China's Foreign Ministry said in a brief statement late on Wednesday.

Mr Li is a former deputy head of the Communist Party's International Department, which is deeply involved in contacts with North Korea's ruling party. The former ambassador, Mr Liu, has gone back to working with the same department.

Mr Li is a German speaker who has previously been ambassador to Myanmar and the Philippines.

North Korean leader Kim Jong Un has yet to visit China, his country's only remaining ally of any importance, since assuming office after his father died in 2011, though he is expected to go to Russia this year.

Ties with China have cooled since Mr Kim took over and then, in 2013, defied international warnings and UN sanctions to conduct a third nuclear test.

China and North Korea were firm allies in the 1950-1953 Korean War, but China has been infuriated by North Korea's nuclear tests and made no secret of its desire for the country to give up its nuclear ambitions.

North Korea has conducted three nuclear tests, the last in February 2013, and is under UN sanctions for defying international warnings not to set off atomic devices in pursuit of a nuclear arsenal.

It often promises to call off nuclear and missile tests in return for steps by the United States to ease tension. It reached a deal in February 2012 with the United States for an arms tests moratorium only to scrap it two months later.