As Ukraine faces down a Russian offensive - and lays the groundwork for an expected fightback of its own in spring - focus is once again turning to whether either side has the capability for a decisive breakthrough.

Despite mass mobilisation and a decision to pull increasingly elderly vehicles out of storage, Russia is still running low on the materiel it needs.

Analysts believe it is continuing to burn through an unsustainable number of artillery shells as it grinds forward around the devastated city of Bakhmut. Even supplies of Iranian kamikaze drones appear to have run short.

So there is little surprise that Western minds are now grappling with how to prevent a potential gamechanger: the involvement of China as a provider of arms.

Beijing, long a supporter of Russia on the sidelines, is closely examining whether it should take a more active role - and begin sending Vladimir Putin's struggling armies the equipment they need for a more sustained and damaging campaign against the Ukrainians. Such a decision could transform the conflict - and give China's manufacturers a crucial testbed as they evaluate weapons amid fears over an invasion of Taiwan.

Last week, the US upped the ante in warning China away from arming Russia in its war on Ukraine.

Secretary of State Antony Blinken told Beijing that Chinese firms and leaders could be on the receiving end of sanctions if they intervene.

"We will not hesitate, for example, to target Chinese companies or individuals that violate our sanctions or otherwise engage in supporting the Russian war effort,” he said on a trip to Kazakhstan.

It was the latest in a series of messages from the US to Beijing, and whether they are heeded will be down to Chinese President Xi Jinping. So far China has denied it is an option.

Yet navigational gear, jet fighter parts and jamming technology and other dual-use equipment have already been shipped from China to Russia, the Wall Street Journal reported, after consulting Russian customs data.