The United States opposes Chinese calls for a ceasefire in Ukraine, saying this would simply consolidate "Russian conquest" and allow the Kremlin to prepare a new offensive, a White House spokesman said Friday.

"We don't support calls for a ceasefire right now," National Security Council spokesman John Kirby told reporters ahead of next week's visit to Moscow by Chinese leader Xi Jinping.

"We certainly don't support calls for a ceasefire that would be called for by the PRC in a meeting in Moscow that would simply benefit Russia," he said, using China's official acronym -- the People's Republic of China.

The United States, which is leading a Western coalition to arm Ukraine and support its defense against the more-than-year-long invasion by Russia, is concerned that making a ceasefire the priority would relieve pressure on Russian forces and give the Kremlin an opportunity to consolidate its grip on swaths of territory.

"A ceasefire now is... effectively the ratification of Russian conquest," Mr Kirby said.

"Russia would be free then to use a ceasefire to only further entrench their positions in Ukraine, to rebuild, refit and refresh their forces so they can restart attacks on Ukraine at a time of their choosing."

"We do not believe this is a step toward a just and durable peace."

Kirby reiterated that President Joe Biden plans to talk by phone with Xi but said that arrangements have not even started.

"There is no call scheduled. While the president has made it clear he wants, he looks forward to another opportunity to speak with President Xi, we're not actively engaged in the logistics of setting that up right now," he said.

"To my knowledge, there's been no outreach to the Chinese to work on the logistics."

US officials are watching closely whether China will extend its diplomatic support for Russia during the war to military assistance, such as ammunition or weaponry.

Mr Kirby said Beijing has not "taken it off the table, but we also haven't seen any indications, any confirmation, that they've made a decision to move in that direction or have actually provided" weapons.