The EU sought Friday to convince China's leaders at a virtual summit not to back Russia in its war on Ukraine as the conflict threatened to hit vital trade ties between the economic superpowers.

EU chiefs Charles Michel and Ursula von der Leyen held talks first with Chinese Premier Li Keqiang ahead of a video conference with President Xi Jinping. 

The discussions -- initially intended to focus on issues like trade and climate change -- have been overshadowed by Western fears of Chinese support for Moscow in its attack on Ukraine. 

The EU and US worry that Beijing's failure to condemn the invasion means it could be willing to help the Kremlin sidestep the impact of sanctions or even supply hardware to aid the war effort.

"The international community notably China and the EU have a mutual responsibility to use their joint influence and diplomacy to bring an end to Russia's war in Ukraine and the associated humanitarian crisis," Michel wrote on Twitter after the first round of the talks.

Wang Lutong, head of European Affairs at China's foreign ministry, said the two sides had "agreed to work together to maintain peace, stability and prosperity in the world."

"On Ukraine, Premier Li Keqiang said that China opposes both a hot war and a cold war; it opposes division of blocs and taking sides," he wrote on Twitter. 

The official also said there was an agreement "to conduct dialogue on energy security and food security, so as to jointly maintain the stability of the world economy."

Frozen trade pact 

The EU's ties with its largest trading partner had already been battered by a stream of tensions ahead of Moscow's assault on Ukraine. 

The annual summit was skipped last year as ties frayed and the ratification of a major investment pact was put on ice.

The talks are usually an effort to deepen trade ties. But the exchange of tit-for-tat sanctions over the plight of China's Uyghur minority, followed by Beijing's trade coercion of EU-member Lithuania over Taiwan, soured the mood.

The downgrade in relations came surprisingly quickly after the EU and China secured the investment deal in late 2020 long sought by Germany.

Human rights concerns, and US pressure on the EU, sapped momentum, sowing distrust and sinking diplomatic ties.

No limits

The tensions over Russia's war on Ukraine now threaten to hit relations harder -- even if the EU for now is shying off threatening sanctions on Beijing if its helps the Kremlin.

In a meeting with Russian counterpart Sergei Lavrov, Chinese Foreign Minister Wang Yi on Wednesday said that "China-Russia cooperation has no limits", repeating a line used by Presidents Vladimir Putin and Xi.

The friendship between Russia and China "is clearly directed towards creating a new world order in which authoritarian great power politics would dominate over the international rule of law," said German MEP Reinhard Buetikofer, a frequent critic of Beijing.

An EU official involved in preparing the summit stressed the importance of China's stance on Russia over all else.

"It has very concrete significance whether China uses or does not use its influence to have ceasefire established, humanitarian corridors established, that it doesn't help or helps to circumvent sanctions," the official said. 

A second official from the bloc insisted that China "has to realise that, while it thinks that (the Russian invasion of Ukraine) has nothing to do with EU-China relations, actually it does".

But Sylvie Bermann, a former French ambassador to both Moscow and Beijing, cautioned: "The idea of detaching China from Russia is a pipe dream."