China has ramped up support for Russia’s war in Ukraine and has begun sending it rifle scopes, tank components, rocket fuel and even satellite imagery, US officials have said.

Vladimir Putin has courted China heavily since his invasion two years ago, but Beijing has always appeared reluctant to be seen propping up his military.

Now, with Russia taking ground in eastern Ukraine, that appears to have changed.

China has also begun sending microelectronics, propellants used in missile production and turbojet engines to Russia, sidestepping Western sanctions.

The warning came as Sergei Lavrov, the Russian foreign minister, prepared to travel to Beijing to discuss the war in Ukraine,

Russia is currently outgunning Ukrainian forces across the frontlines because the EU and the US have struggled to supply promised ammunition. By contrast, the Kremlin has accelerated its weapons production, switching consumer-based factories to arms manufacturing and signing deals with Iran and North Korea for supplies of drones and artillery shells.

US officials told Bloomberg News on condition of anonymity that US Secretary of State Antony Blinken had briefed European allies this week on China’s recent increased support for Russia.

Analysts said China may have switched to a policy of quietly supporting the Kremlin’s war machine.

“Beijing doesn’t give arms because it fears US secondary sanctions and wants to develop EU relations, but still silently supplies machinery that’s important for Russia to sustain its arms production,” said Carl Bildt, co-chair of the European Council on Foreign Relations think tank and a former Swedish prime minister.

The Kremlin has said that Putin plans to visit China in May. On a trip to Moscow last year, Putin and Chinese leader Xi Jinping declared a “no limits” partnership.

US-led sanctions on Russia have hit the Kremlin’s industrial base but they have also been more leaky than planners had hoped.

One of the main gateways for products into Russia is through former Soviet states in Central Asia and the South Caucasus but Hong Kong has also become an important route, especially for vital microchips, and the US has already slapped secondary sanctions on several Chinese companies.