MOSCOW, May 6 (Reuters) - Russia's Vladimir Putin and

China's Xi Jinping will discuss the "most sensitive" issues,

including energy cooperation and a proposed Power of Siberia 2

gas pipeline to China, Kremlin aide Yuri Ushakov said on

Tuesday.

Xi will start an official four-day visit to Moscow on

Wednesday and will be among a number of the global leaders,

invited in the Russian capital to celebrate the 80th anniversary

of the defeat of Nazi Germany.

Ushakov told reporters that Russia was the largest oil and

gas supplier to China, and gave an affirmative answer to a

question if the Power of Siberia 2 pipeline will be discussed.

Russia proposed the pipeline via Mongolia years ago but the

plan has gained urgency as Moscow looks to Beijing to replace

Europe as its major gas customer.

However, China is not expected to need additional gas supply

until after 2030, experts say. One of the key issues yet to be

agreed to start the construction of the pipeline is the price of

natural gas.

The 2,600-km pipeline could carry 50 billion cubic metres

(bcm) of gas a year, slightly less than the now defunct Nord

Stream 1 pipeline linking Russia to Germany under the Baltic

Sea.