The diplomat has held a series of meetings with Belgian, NATO and EU officials over the past two days. During the talks, he provided allies with details of China's "substantial support" for Russia's military-industrial base and the battlefield implications in Ukraine.
Much of this support, he said, was being provided covertly.
"We have asked our European counterparts... to do more and to join us in making public statements of concern and cautious signs of willingness to take action to express our displeasure," Campbell said.
He also noted that simply monitoring certain financial institutions more closely and communicating clearly could have "significant consequences," as China and Russia closely monitor the financial system and worry about potential moves against them.
According to Campbell, Russia is increasingly cooperating with China on research and support in areas such as submarines, aircraft design, particularly stealth technology, and missile capabilities.
For example, the diplomat noted, Chinese advances in submarines could undermine the current undersea advantages of the United States. And Russia's assistance in improving certain Chinese military capabilities would have a "significant, negative and troubling impact" on other countries in the Indo-Pacific region.
Campbell noted that the United States, the EU, and NATO partners are increasingly aligning their policies toward China.
"There are some countries, a few, that may be lagging behind and have different views. But I would say that most of both the EU and NATO are moving in the direction of increasing concern about various steps that China is taking," the US deputy secretary of state said.