China has surged sales to Russia of machine tools, microelectronics and other technology that Moscow in turn is using to produce missiles, tanks, aircraft and other weaponry for use in its war against Ukraine, according to a U.S. assessment.

Two senior Biden administration officials, who discussed the sensitive findings Friday on the condition of anonymity, said that in 2023 about 90% of Russia’s microelectronics came from China. Russia has used those to make missiles, tanks and aircraft. Nearly 70% of Russia’s approximately $900 million in machine tool imports in the last quarter of 2023 came from China.

Chinese and Russian entities have also been working to jointly produce unmanned aerial vehicles inside Russia, and Chinese companies are likely providing Russia with the nitrocellulose used in the manufacture of ammunition, the officials said. China-based companies Wuhan Global Sensor Technology Company, Wuhan Tongsheng Technology Company and Hikvision are providing optical components for use in Russian tanks and armored vehicles.

The officials said that Russia has received military optics for use in tanks and armored vehicles manufactured by Chinese firms iRay Technology and North China Research Institute of Electro-Optics, and that China has been providing Russia with UAV engines and turbojet engines for cruise missiles.

Russia’s semiconductor imports from China jumped from $200 million in 2021 to over $500 million in 2022, according to Russian customs data analyzed by the Free Russia Foundation, a group that advocates for civil society development.