China's economic ties with Russia have helped limit the effect of punishing Western sanctions imposed over Moscow's invasion of Ukraine, a US intelligence report said Thursday.

China "has become an even more critical economic partner for Russia since its invasion of Ukraine in February 2022," says the unclassified report, which was released by Democratic lawmakers.

"Beijing is pursuing a variety of economic support mechanisms for Russia that mitigate both the impact of Western sanctions and export controls," it says.

China has boosted energy imports from Russia and has provided tankers and insurance coverage to move crude oil.

The two sides have also "increased the share of bilateral trade settled in yuan" as well as "expanding their use of domestic payment systems," which helps "Russian entities to conduct financial transactions unfettered of Western interdiction."

The report says Beijing has probably supplied Moscow with dual-use civilian-military equipment employed in Ukraine, but notes that it is "difficult to ascertain the extent to which (China) has helped Russia evade and circumvent sanctions and export controls."

Russia failed in its attempt to take Kyiv and decapitate the country's government in the early days of the war, but seized swathes of other territory that Ukrainian troops are fighting to retake.

Beijing says it is a neutral party in the conflict but has been criticized by Western countries for refusing to condemn Moscow and for its continued ties with Russia.