President Joe Biden will seek Friday to coax Xi Jinping into ratcheting up pressure on Moscow to end its war in Ukraine, in his first phone call with the Chinese president since the invasion began.

U.S. officials have struggled to discern China’s position on the war, as Beijing has both avoided public criticism of Russian President Vladimir Putin and offered rhetorical support for Ukraine. 

White House National Security Adviser Jake Sullivan met with China’s top diplomat, Politburo member Yang Jiechi, in Rome on Monday for about six hours, but neither side announced any firm outcomes of the talks.

Publicly, China has said it’s trying to help foster diplomacy to halt the fighting. But U.S. officials are concerned Beijing may help Russia evade Western economic sanctions or even provide it weapons, after the two countries declared just before the invasion that their friendship had “no forbidden zones.”

White House Press Secretary Jen Psaki said in a statement Thursday that the call “is part of our ongoing efforts to maintain open lines of communication.” 

“The two leaders will discuss managing the competition between our two countries as well as Russia’s war against Ukraine and other issues of mutual concern,” Psaki said.

The call will be Biden and Xi’s first conversation since November, when they met virtually for nearly four hours.

The Biden administration has tried to persuade Beijing not to contribute to the war. The White House’s view is that China has tacitly supported Russia’s invasion, and the U.S. has repeatedly warned Xi’s government that it would suffer consequences if it provides direct support for the Kremlin -- including in Sullivan’s meeting with Yang.

China denies it has supported the war and has also denied U.S. reports that Russia requested financial and military aid shortly after the invasion, calling them disinformation. The Kremlin has also denied those reports.

U.S. officials, for their part, have expressed outrage that China has helped amplify Russian claims of a U.S. and Ukrainian biological weapons project -- disinformation the White House regards as a possible pretext for the Kremlin to order its own attack with chemical or biological weapons.

Yet China’s ambassador to Ukraine delivered some of Beijing’s most supportive comments yet toward the war-torn nation this week, remarks that were endorsed Thursday by China’s foreign ministry.

Ambassador Fan Xianrong had told Lviv Governor Maksym Kozytskyi during a meeting Monday that China was a “friendly country for the Ukrainian people” and would “never attack Ukraine,” according to a summary posted on the Lviv government’s website. He went on to praise the strength and unity demonstrated by the Ukrainian people, in an apparent reference to their resistance to the ongoing invasion. 

Asked about Fan’s comments at a news conference Thursday, Foreign Ministry spokesman Zhao Lijian said: “China surely supports these remarks by our ambassador in Ukraine. China supports all efforts that are conducive to easing the situation and for a political settlement.”

A day earlier, Zhao had said he was “not aware” of the comments, fueling uncertainty about whether Fan was expressing the central government’s position.

The relationship between the U.S. and China, the world’s two largest economies, remains fraught overall, as they continue to spar over economic policies and human rights issues. The Biden administration has promised actions against what it considers China’s harmful non-market economic practices, but has yet to announce the moves.

Biden and Xi last spoke in November, during a video conference in which Biden stressed that the two superpowers need to establish guardrails to ensure their economic and foreign policy competition doesn’t veer into armed conflict.