Tensions have been rising a year into the conflict as the United States has accused China of considering arming Russia in its fight against Ukraine.

Secretary of State Antony Blinken made these accusations at a time when US-China relations have been sorely strained by Washington’s shooting down this month of what he said was a large Chinese spy balloon.

The European Union has also sounded the alarm about ammunition in the Ukraine conflict, stating that the severe ammunition shortage facing Ukrainian forces must be overcome in a matter of weeks.

Blinken told CBS that China was now “considering providing lethal support” to Moscow, from “ammunition to the weapons themselves.”

“We have made it very clear to them that this would cause a serious problem for us and in our relationship,” he added.

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

In addition, EU foreign policy head Josep Borrell delivered a dire warning at the Munich conference about the decreasing supplies of bullets and comparable weaponry in Ukraine’s struggle against the Russian invasion.

“We are going to accelerate our military support to Ukraine because Ukraine is in a critical situation from the point of view of available ammunition,” Borrell said. “This ammunition shortage has to be resolved quickly; it is a matter of weeks.”

Wang reiterated that Beijing was playing a constructive role and would encourage dialogue and possible peace talks amid fears that China was tightening ties with Russia despite the war.

Speaking on ABC on Sunday, Blinken emphasized that in March of last year, US Vice President Joseph Biden had cautioned Xi Jinping, his Chinese counterpart, not to supply arms to Russia.

An administration source said that since then, “China has been careful not to cross that line, notably by banning the supply of lethal weapons systems for use on the battlefield.”

One of the most prominent Republicans in the United States, Senator Lindsey Graham, was also in attendance at the Munich meeting and warned that supplying Russia with weapons from China would be a huge mistake.

Graham, a well-known hawk on foreign policy, also stated that he had solid indicators that the United States would soon disclose intentions to train Ukrainian fighter pilots, marking another step in the slow escalation of Western efforts to arm Ukraine.

Graham stated that, in his judgment, the United States should label Russia a state supporter of terrorism for its actions in Ukraine, which would result in penalties against China and any other nation that supplies it with arms.

Blinken’s meeting with Wang, the highest-level encounter between the two nations since the United States shot down a Chinese balloon on February 4, did not appear to ease current tensions.

“I just told him that this was unacceptable and it couldn’t happen again,” Blinken told CBS of the balloon incident.

On Saturday, Wang dismissed the US accusations of high-altitude spying in unusually harsh language, calling them “hysterical and absurd.” Blinken said his counterpart had not offered him “any apology.”

The harsh 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 against the country’s civilian population.

Biden will speak in Warsaw on Tuesday to praise NATO’s unprecedented effort to help Ukrainians save their country, marking the first year of the war.

That same day, President Vladimir Putin will deliver his own speech in Moscow, three days after February 24, the date Russian tanks stormed Ukraine.