President Xi Jinping on Wednesday assured Vladimir Putin of China's support on Russian "sovereignty and security" -- leading Washington to warn Beijing it risked ending up "on the wrong side of history".
China has refused to condemn Moscow's massive military assault on Ukraine and has been accused of providing diplomatic cover for Russia by blasting Western sanctions and arms sales to Kyiv.
China is "willing to continue to offer mutual support (to Russia) on issues concerning core interests and major concerns such as sovereignty and security," state broadcaster CCTV reported Xi as saying during a call with President Putin.
It was the second reported call between the two leaders since Putin launched his invasion of Ukraine on February 24.
According to CCTV, Xi praised the "good momentum of development" in bilateral relations since the start of the year "in the face of global turmoil and changes".
Beijing was willing to "intensify strategic coordination between the two countries", Xi reportedly said.
The Kremlin said the two leaders had agreed to ramp up economic cooperation in the face of "unlawful" Western sanctions.
"It was agreed to expand cooperation in the energy, financial, industrial, transport and other areas, taking into account the situation in the global economy that has become more complicated due to the unlawful sanctions policy of the West," the Kremlin said following the phone call.
But the United States swiftly weighed in with a frosty retort to Beijing's expressed alignment with Moscow.
"China claims to be neutral, but its behavior makes clear that it is still investing in close ties to Russia," a State Department spokesperson said.
Washington was "monitoring China's activity closely," including how, nearly four months into Russia's war in Ukraine, the Asian giant was "still echoing Russian propaganda around the world" and suggesting Moscow's atrocities in Ukraine were "staged," the official said.
"Nations that side with Vladimir Putin will inevitably find themselves on the wrong side of history."
- 'No limits' relationship -
The West has adopted unprecedented sanctions against Russia in retaliation for its invasion of Ukraine, and Moscow considers that Europe and the United States have thus caused a global economic slowdown.
Moscow is also looking for new markets and suppliers to replace the major foreign firms that left Russia following the invasion.
The European Union and the United States have warned that any backing from Beijing for Russia's war, or help for Moscow to dodge Western sanctions, would damage ties.
China and India are two major economies that have not taken part in retaliatory measures against Moscow.
In the eyes of Chinese officials, the Europeans have allowed themselves to be sucked into backing Ukraine, at Washington's initiative, in a move contrary to their interests as Russian gas consumers.
Once bitter Cold War enemies, Beijing and Moscow have stepped up cooperation in recent years as a counterbalance to what they see as US global dominance.
The pair have drawn closer in the political, trade and military spheres as part of what they call a "no limits" relationship.
Last week they unveiled the first road bridge linking the two countries, connecting the far eastern Russian city of Blagoveshchensk with the northern Chinese city of Heihe.
The leaders' call Wednesday fell on Xi's 69th birthday and was their first reported communication since the day after Russia launched its Ukraine invasion.
Beijing is Moscow's largest trading partner, with trade volumes last year hitting $147 billion, according to Chinese customs data.