The United States has not seen any evidence that China is providing direct military support to Russia, which is waging an aggressive war against Ukraine.

"We have not seen any evidence that they (China) provide direct military air to Russia," US National Security Advisor Jake Sullivan said at a briefing.

At the same time, Sullivan added, the United States has expressed concerns about Beijing's efforts to strengthen Russia's military-industrial base, mentioning that US Secretary of State Antony Blinken spoke about this in Europe last week.

Earlier, the US State Department confirmed that Blinken expressed concerns in discussions with allies about the nature of cooperation between China and Russia, which, in particular, enhances the ability of the Russian military-industrial complex to continue to support the Russian army.

Earlier, the Financial Times, citing unnamed officials, reported that US Secretary of State Antony Blinken said in communication with counterparts in the EU and NATO that China's assistance to Russia was "at a concerning scale", especially when it comes to producing optical equipment, propellants and space equipment. 

Meanwhile, Janet Yellen, US Secretary of the Treasury, said that she had "difficult conversations" about Ukraine during her four-day visit to China, and warned China that Chinese companies cooperating with the Russian military-industrial complex might suffer serious consequences.