'Best relationship ever'

An agreement signed by Russian Defense Minister Sergey Shoigu and his Chinese counterpart Wei Fenghe in November capped a year that has seen unprecedented growth in military cooperation, including large drills in China's northwest in August, when Russian troops became the first foreign forces to join a regular Chinese drill. The year also witnessed announcements for collaboration on the design of aircraft, including helicopters, and some types of high-tech weaponry.

"It's the strongest, closest and best relationship that the two countries have had since at least the mid-1950s－and possibly ever," said Nigel Gould-Davies, a senior fellow for Russia and Eurasia at the International Institute for Strategic Studies, a think tank on global security headquartered in London.

Despite the warmth in the bilateral relationship, Ostrovsky said: "Russia and China, however, have said that they have no intention to create a military bloc. Yet the good neighbor agreement on friendship and cooperation, originally signed in 2001, has been extended for five years. I think that it has to be made clear to the US that if they continue to step up the pressure, then an agreement on military cooperation will be signed."

Rather than enter into a military alliance, Russia and China prefer to stand back-to-back and shoulder-to-shoulder in the face of external pressures, he said.

Vladimir Batyuk, head of the Political and Military Research Center at the Institute for the US and Canadian Studies of the Russian Academy of Sciences, said that from the basis of a nonbinding strategic partnership, Russia and China are moving to a new stage of cooperation.

On foreign policy, Beijing and Moscow share similar approaches on Iran, Syria and Venezuela, and recently revived a push to lift sanctions on the Democratic People's Republic of Korea, observers say.

For China, Russia is the second-largest source of oil imports. China is Russia's top trading partner and a key source of investment in its energy projects, including the Yamal liquefied natural gas plant in the Arctic Circle and the Power of Siberia pipeline－at $55 billion, the biggest gas project in Russia.

In the first 11 months of 2021, Sino-Russian trade reached a historic high of 843.41 billion yuan ($132.5 billion), a 24 percent year-on-year jump, according to China's General Administration of Customs.

Vasily Kashin, the head of the Center for Comprehensive European and International Studies at the Higher School of Economics, said the two countries significantly increased cooperation across the political, military and economic spheres in 2021.

"At the same time, tensions were growing both in Eastern Europe and in Eastern Asia. And each side separately was conducting its complicated dialogue with the US in recent months," he said.

Russian-Chinese relations are built on the finest nuances and reflect the situation prevailing in each country, said Alexey Maslov, director of the Institute of Asian and African Studies.