"So far, we have no such evidence, but this needs to be monitored daily," von der Leyen told a press conference alongside German Chancellor Olaf Scholz.
When asked whether Brussels would press sanctions against China if such fact was confirmed, the European Commission chief said that it would be addressed "only when it becomes reality."
The German chancellor chimed in saying that China should never supply weapons to Russia and that Beijing had said it would not supply any.
In late February, US State Secretary Antony Blinken said that China mulled the possibility to provide "lethal" military assistance to Russia, including either weapons or ammunition. Until now, he said, private Chinese companies have provided Russia with only "non-lethal" support. He also threatened China with "real consequences," should it send military supplies to Russia.
Chinese Foreign Ministry spokesman Wang Wenbin said it was the United States who was funneling weapons to Ukraine and urged Washington to "stop shifting responsibility and spreading false information."