China is working as Russian President Vladimir Putin's "silent partner" in his war against Ukraine, CIA Director William Burns said Thursday.

In his first public address since assuming the agency's top role, Burns did not elaborate on China's support but said Beijing presents the CIA with "the most profound test" it has faced in its 75-year history, "lacking in neither ambition nor capability."

"It seeks to overtake us in literally every domain, from economic strength to military power, and from space to cyberspace," he said. "As an intelligence service, we have never had to deal with an adversary with more reach in more domains."

Turning to Russia's war against Ukraine, he said the scenes of devastation emerging from the besieged city of Mariupol and Russia-occupied Kharkiv "are sadly reminiscent" of the 1994-1995 Battle of Grozny, where Russian forces brutally clamped down on the Chechen capital, leveling dozens of square blocks.

"But Ukrainian will is unbroken, and Putin's Russia has inflicted massive material and reputational damage on itself," he said.

The U.S. has repeatedly criticized China for refusing to condemn Russia's assault on Ukraine and vocally warned Beijing against providing the Kremlin with military support to reinforce its offensive.

According to United Nations estimates, at least 1,964 civilians have been killed and 2,613 injured in Ukraine since Russia began its war, with the true figure feared to be much higher.

More than 4.7 million Ukrainians have fled to other countries since the beginning of the war that started Feb. 24, with over 7 million more internally displaced, said the U.N. High Commissioner for Refugees.