EU diplomatic chief Josep Borrell said Monday that he had warned Wang Yi, head of the office of the CPC Central Committee's Foreign Affairs Commission, against supplying Chinese weapons to Russia.

"I had a long conversation with Wang Yi ... And I expressed our serious concern about (the possibility of) China supplying weapons to Russia. And I asked him not to do that. I expressed not only our concern, but that it would be a red line for our relations," Borrell told reporters before the meeting of EU foreign ministers.

According to him, Wang Yi "said they would not do it."

"But we remain vigilant," Borrell added.

Earlier, U.S. Secretary of State Antony Blinken said Washington is watching closely to ensure that China does not provide military assistance to Russia.