China is helping Russia undertake its biggest military expansion since Soviet times, US officials said Friday, stepping up public pressure as concerns rise over Ukraine.

US officials are hoping the release of the intelligence will encourage European allies to press China, as Chancellor Olaf Scholz heads to Beijing this weekend and Group of Seven foreign ministers meet next week in Italy.

Unveiling US findings, officials said China was helping Russia on a range of areas including the joint production of drones, space-based capabilities and machine-tool exports vital for producing ballistic missiles.

China has been the key factor in revitalizing Russia's defense industrial base "which had otherwise suffered significant setbacks" since Russia's invasion of Ukraine, a senior US official told reporters on condition of anonymity.

"Russia is undertaking its most ambitious defense expansion since the Soviet era and on a faster timeline than we believed possible early on in this conflict," the official said.

"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 to stop helping Russia reconstitute its military industrial base," the official said, referring to the People's Republic of China. 

"Russia would struggle to sustain its war effort without PRC inputs," he said.

US officials said that China provided more than 70 percent of the $900 million in machine tools -- likely used to build ballistic missiles -- imported in the last quarter of 2023 by Russia.

US officials also said that 90 percent of Russia's microelectronics imports -- used to produce missiles, tanks and aircraft -- came from China last year.

China walks fine line

The United States has repeatedly warned China against supporting Russia and both Chinese and US officials say Beijing has stopped short of directly providing weapons to Russia, which has turned to heavily sanctioned North Korea and Iran to replenish arms supply.

US officials believe that China, anxious after its Russian allies' early setbacks on the battlefield, has instead focused on sending material that ostensibly has non-military uses.

President Joe Biden's administration is hoping that European powers can make the difference in persuading China, which is facing economic headwinds and is sensitive about trade pressure.

Secretary of State Antony Blinken is expected to make the case on China's ties with Russia as he meets top diplomats of other industrial democracies at the G7 talks in Capri, Italy.

Blinken is also planning a visit in the coming weeks to China, on the heels of a trip by Treasury Secretary Janet Yellen.

The administration hopes that such dialogue, including a recent telephone call between Biden and Chinese President Xi Jinping, can help contain tensions between the world's two largest economies but US officials have stressed they will still press on concerns.

Deputy Secretary of State Kurt Campbell said this week that Europe's stability was the top interest historically of the United States and that it would hold China accountable if Russia makes gains.

Ukraine has suffered its first battlefield setbacks in months as its forces ration ammunition, with the United States failing to authorize new support due to a deadlock in the Republican-led House of Representatives.