BEIJING - Russian Prime Minister Dmitry Medvedev, who is on a two-day official visit to China, said the two countries on Tuesday signed an agreement by which Russia will supply an additional 10 million tonnes of crude oil to China each year over the next 10 years.

"(We) will supply an additional 10 million tonnes of crude oil each year (to China), which will be done by Russia's biggest oil company Rosneft. It means 100 million tonnes in the next 10 years, worth a total of $85 billion," Medvedev said during an online chat with netizens from across China via Xinhuanet.com, the official website of Xinhua.

"It is a big sum of money to any country, even to China. It testifies to the fact that we have reached a higher and a brand new level of cooperation," he said.

Earlier in the day, Chinese Premier Li Keqiang and Medvedev co-chaired the 18th regular meeting between the Chinese and Russian heads of government to boost bilateral ties. They also witnessed the signing of an array of documents.

Another example of Russian-Sino cooperation, Medvedev said, was that the two countries will jointly construct a joint-venture oil refinery in Tianjin, which will be able to refine 16 million tonnes of crude oil each year.

"It is a high-tech project, which will employ the most advanced oil refinery technologies," he said.

The Tianjin refinery is jointly set up by China National Petroleum Corporation (CNPC), the country's largest oil and gas producer and supplier, and Rosneft. CNPC holds a 49 percent stake while Rosneft holds the remaining 51 percent.

Chinese official statistics showed China imported 24.33 million tonnes of crude oil from Russia in 2012.

In June, CNPC and Rosneft signed a long-term agreement in St Petersburg for oil deliveries, involving supplies of 365 million tonnes of oil to China in the next 25 years, with an estimated value of $270 billion.