Russia warns UK that troop deployment in Ukraine would be 'declaration of war'

A senior ally of Russian President Vladimir Putin has warned the U.K. that putting boots on the ground in Ukraine would amount to a declaration of war against Russia.

Dmitry Medvedev, the deputy chair of the Security Council of Russia, took aim at the country in a post Friday on X as U.K. Prime Minister Rishi Sunak was arriving in Kyiv to announce a major funding package for Ukraine. 

The U.K. will provide around $3.2 billion of military aid to Ukraine over the coming year, its largest annual commitment since Russia's invasion nearly two years ago.

Medvedev, who served as Russian president from 2008 and 2012, also posited a hypothetical situation where Sunak would come under military fire while in the Ukrainian capital. 

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"The British Prime Minister Rishi Sunak has arrived in Kiev to sign a ‘historic UK-Ukraine Agreement on Security Cooperation,’" Medvedev wrote.

"What would [the] Western public say, if the British representatives happened to be bombarded with cluster ammunition in the center of Kiev, just as was the case with our innocent civilians in Belgorod?"

Medvedev was referring to a Dec. 30 attack on Russian civilians in the city of Belgorod, in southern Russia near the Ukrainian border, where at least 20 people were killed, including two children, and 111 injured in what it called an "indiscriminate" Ukrainian strike using cluster bombs.

Medvedev then went on to warn the U.K. about potentially deploying a military contingent in Ukraine. 

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"And I also hope that our archenemies, the impudent British understand that officially stationing their troops in Ukraine would mean declaration of war against our country," Medvedev wrote.

Ukrainian news outlet RBC-Ukraine quoted unnamed sources as saying Ukrainian forces had directed fire at military targets in Belgorod in response to the massive Russian bombardment of Ukrainian cities the previous day.

On Friday, Sunak said that the U.K. "will not falter" in its commitment to help Ukraine forces stand up to Putin’s full-scale invasion.

"Today we are going further — increasing our military aid, delivering thousands of cutting-edge drones, and signing a historic new Security Agreement to provide Ukraine with the assurances it needs for the long term," Sunak said.

Ukraine and Russia are seeking to replenish their arsenals this year, military analysts say, in anticipation of possible major ground offensives in 2025.

On X, Sunak wrote that Britain is with Ukraine for "as long as it takes."

Reuters contributed to this report.