WASHINGTON, April 12 (Reuters) - China is backing

Russia's war effort in Ukraine by helping Moscow in its biggest

military buildup since the Soviet era, providing drone and

missile technology, satellite imagery and machine tools, senior

U.S. officials said on Friday.

However, the Chinese Embassy in the U.S. said it has not

provided weaponry to any party, adding that it is "not a

producer of or party involved in the Ukraine crisis."

The officials, speaking on condition of anonymity, said U.S.

President Joe Biden raised the issue with Chinese President Xi

Jinping in their recent phone call and that it is a topic of

discussion with U.S. allies in Europe and around the world.

One official said Chinese materials are filing critical gaps

in Russia's defense production cycle and helping Moscow

undertake its "most ambitious defense expansion since the Soviet

era and on a faster timeline than we believed possible early on

in this conflict."

"Our view is that one of the most game-changing moves

available to us at this time to support Ukraine is to persuade

the PRC (China) to stop helping Russia reconstitute its military

industrial base. Russia would struggle to sustain its war effort

without PRC input," the official said.

A Chinese embassy spokesperson told Reuters that normal

trade between China and Russia should not be interfered or

restricted.

"We urge the U.S. side to refrain from disparaging and

scapegoating the normal relationship between China and Russia,"

Liu Pengyu said.

Some of the information provided by the U.S. officials in a

small briefing with reporters was based on declassified

intelligence. They sketched a wide array of ways China is

helping Russia's two-year war against Ukraine without providing

lethal assistance.

President Joe Biden has been pressuring Republicans who

control the U.S. House of Representatives to approve a major

infusion of funding for providing weapons to Ukraine as it

struggles to fend off the Russians.

The U.S. and its allies have also been more blunt about

confronting Chinese aggression in the South China Sea and

against self-ruled Taiwan.

China complained about what it viewed as anti-China rhetoric

emanating from Biden's talks this week with the leaders of Japan

and the Philippines, prompting a denial from the White House.

The Russians have likely used machine tool imports from

China to increase its ballistic missile production, the

officials said. They cited Dalian Machine Tool Group, one of

China's leading machine tool manufacturers, as one company

supplying Russia.

In 2023, 90% of Russia's microelectronics imports came from

China, which Russia has used to produce missiles, tanks and

aircraft, the officials said.

They said that Chinese companies such as Wuhan Global Sensor

Technology Co, Wuhan Tongsheng Technology Co Ltd and Hikvision

are providing Chinese optical components for use in

Russian systems, including tanks and armored vehicles.

In addition, Russia has received military optics for tanks

and armored vehicles that Chinese firms Yantai-based IRay

Technology Co Ltd and North China Research Institute of

Electro-Optics manufacture, they said.

The officials also said China has provided Russia with drone

engines and turbojet engines for cruise missiles, and that

Chinese and Russian entities have been working to jointly

produce drones inside Russia.

Chinese companies are likely providing Russia with

nitrocellulose to make propellants for weapons, helping Russia

rapidly expand its capacity to make key munitions like artillery

rounds, they added.

The U.S. officials also said China is helping Russia improve

its satellite and other space-based capabilities for use in

Ukraine, increasing the Russian threat across Europe. And they

said the U.S. has information China is providing imagery to

Russia for its war on Ukraine.