The US says China will face harsh "consequences" if it aids Russia in its invasion of Ukraine.
Unnamed officials have told multiple US news outlets that Russia asked China to provide military assistance after it began the invasion.
The Chinese embassy in Washington said it was not aware of this request.
The warning comes ahead of a meeting in Rome today between top US and China officials.
Ukraine's President has repeated calls for a no-fly zone.
35 people were killed in an airstrike on a military base close to the Polish border yesterday.
Meanwhile, Unicef is calling for the immediate cessation of all attacks on healthcare in Ukraine.
It says they're killing and causing serious injuries to patients and health workers and destroying vital health infrastructure.
It says to target the most vulnerable including babies and pregnant women is an act of cruelty.
Unicef Chief Executive, Peter Power says these attacks must stop:
"We are deeply concerned about the attacks on critical resources in Ukraine," he added.
"There is absolutely no need whatsoever for these attacks and is leading to a critical humanitarian situation on the ground."
