Vučić's opaque comment comes amid continuing multilateral negotiations to end Russia's invasion and shore up Ukraine's resistance.
In remarks caught on a hot microphone, Serbian President Aleksandar Vučić appeared to suggest he had received a "message from Moscow" as he arrived in Brussels for talks with top European Union officials.
Vučić was walking next to EU Commission President Ursula von der Leyen at the Berlaymont building in Brussels for a family picture on Thursday when he appeared to whisper: "I got a message from Moscow now."
The exchange was abruptly halted by von der Leyen, who appeared to whisper: "Let's ... let's wait until."
The two were accompanied by EU Council President António Costa, and exited together after taking a picture.
It is unclear what message from Moscow Vučić was referring to. The Serbian president is one of the few European leaders who maintains a communications channel with the Kremlin, as the EU broke off diplomatic ties with Moscow after its full-scale invasion of Ukraine in 2022.
Vučić was in Brussels on Wednesday for a Serbia–EU bilateral meeting to discuss, among other themes, the country's EU membership bid.
Meanwhile, negotiations to end Russia's war in Ukraine continue.
On Wednesday, Ukrainian President Volodymyr Zelenskyy said he would soon present the US with more "refined documents" on a proposal to end the war, with input from Kyiv's European partners.
US President Donald Trump, meanwhile, suggested this week that he could travel to Europe take a meeting on the negotiations, but only if it takes the process further.
"They would like us to go to a meeting over the weekend in Europe, and we’ll make a determination, depending on what they come back with. We don’t want to be wasting time," Trump said.
A meeting of the "Coalition of the Willing," a group of more than 30 countries led by France and the UK, is scheduled for Thursday. The French president's office said this is a critical moment for Ukraine, its people and the security of Europe.