With the conflict marking its first year this week, the European Union also sounded an alarm over munitions -- saying that Ukraine's severe ammunition shortages had to be overcome within weeks.

Blinken told CBS that China was "considering providing lethal support" ranging "from ammunition to the weapons themselves."

He made similar comments in a series of interviews from Germany, where on Saturday he attended the Munich Security Conference and met with his Chinese counterpart, Wang Yi.

He told Wang then that "if China provides material support to Russia or assistance with systemic sanctions evasion," there will be consequences, a US official said.

Also at the Munich conference, EU foreign policy chief Josep Borrell issued a stark warning about Ukraine's dwindling supplies of bullets and similar munitions as it fights back against Russia's invasion.

"Ukraine is in a critical situation from the point of view with ammunition available," he said. "This shortage of ammunition has to resolve quickly, it's a matter of weeks."

- Strained ties -

The US warnings appeared to be among the clearest yet that China might be poised to help arm Russia.

They also came at a time when already strained US-Chinese relations have been further tested by Washington's shooting down of what it said was a large Chinese spy balloon.

Appearing Sunday on ABC, Blinken emphasized that US President Joe Biden had warned his Chinese counterpart, Xi Jinping, as long ago as last March against sending weapons to Russia.

Since that time, "China has been careful not to cross that line, including by holding off on selling lethal weapons systems for use on the battlefield," according to an administration source familiar with the issue.

A top Republican senator who also attended the Munich conference, Lindsey Graham, said it would be a serious mistake for China to provide Russia with weapons.

Doing so now, he said, would be "dumber than dirt. It would be like buying a ticket on the Titanic after you saw the movie."

- 'No apology' -

Graham, known as a well-informed foreign policy hawk, also said he had strong indications that the US will soon announce plans to train Ukrainian fighter pilots, which would represent a further step in the West's gradually escalating efforts to arm Ukraine.

Graham said he believed the United States should declare Russia a state sponsor of terror for its actions in Ukraine -- which would mean that China or any other country supplying it with arms would face sanctions.

Blinken's meeting with Wang -- the highest-level encounter between the countries since US jets shot down the Chinese balloon on February 4 -- did not appear to ease tensions.

"I told him quite simply that that was unacceptable and can never happen again," Blinken told CBS about the balloon incident.

Wang on Saturday dismissed the US allegations of high-altitude spying in uncharacteristically strong language, calling them "hysterical and absurd."

Blinken said Sunday that his counterpart had offered him "no apology."

The tough-sounding exchanges came a day after US Vice President Kamala Harris said in Munich that Russia had committed "crimes against humanity" in Ukraine through "widespread and systemic" attacks on the country's civilian population.