China is sending “lethal aid” to Russia for use in its war against Ukraine, Britain’s defence secretary, Grant Shapps, has said, in comments that were challenged by Joe Biden’s national security adviser, Jake Sullivan.

Shapps used a speech at the London Defence Conference on Wednesday to say: “Today I can reveal that we have evidence that Russia and China are collaborating on combat equipment for use in Ukraine.

As part of his call for Nato to “wake up” and bolster defence spending alliance-wide, he added: “US and British defence intelligence can reveal that lethal aid is now flying from China to Russia and into Ukraine.

“And this is new intelligence which leads me to be able to declassify and reveal this fact today. I think it’s quite significant.”

Shapps did not provide evidence to support his assertion. But he said there had been a 64% increase growth in trade between the countries since the start of the Ukraine and “they are covering each other’s back”.

“It’s time for the world to wake up. And that means translating this moment to concrete plans and capabilities. And that starts with laying the foundations for an alliance-wide increase in spending on our collective deterrent,” he said.

Sullivan appeared to take issue with some of Shapps’s comments. He said the possibility that China might “provide weapons directly – lethal assistance – to Russia” had been a concern earlier, but that “we have not seen that to date”.

The US did however have a “concern about what China’s doing to fuel Russia’s war machine, not giving weapons directly, but providing inputs to Russia’s defence industrial base”, he added.

China and Russia’s strategic partnership has grown closer since the invasion of Ukraine, and US officials say Beijing continues to supply Moscow with key components it needs for its war machine. Its purchase of Russian oil and gas has helped boost the Russian economy.

However, the US believes Beijing has stopped short of directly providing weapons to Russia, which has turned to heavily sanctioned North Korea and Iran to replenish its arms supply.

Chinese president Xi Jinping welcomed Russian counterpart Vladimir Putin to Beijing earlier this month, where the two leaders put on a strong show of unity. Xi said in a statement following talks with Putin that they agreed on the need for a “political solution” to resolve the war.

Last month, Julianne Smith, the US ambassador to Nato, told Politico that China was continuing to sell related supplies such as drone technology and gunpowder ingredients to Russia. “The PRC [People’s Republic of China] cannot claim to be entirely neutral in this case, they are in fact picking a side.

“If they were not providing some of these components, or this materiel support, Russia would be in a very different situation and would have trouble pursuing some of these acts of aggression.”

The Chinese embassy in London did not immediately respond to a request for comment on Shapps’s remarks.

With PA, Reuters and Agence France-Presse