Moscow would consider the open deployment of British troops to Ukraine as a “declaration of war,” former Russian President Dmitry Medvedev has warned. He was responding to a visit to Kiev on Friday by UK Prime Minister Rishi Sunak, who is set to sign a security agreement with Ukrainian President Vladimir Zelensky.

Sunak’s arrival in the Ukrainian capital is meant to “set out a major new package of support and reaffirm the close UK-Ukraine partnership,” his office said in a statement. The security document is a follow-up to agreements reached by G7 and NATO members last year, it noted. The statement did not mention any plans for a British military deployment in Ukraine.

“[The deal] formalizes a range of support the UK has been and will continue to provide for Ukraine’s security, including intelligence sharing, cyber security, medical and military training, and defense industrial cooperation,” Downing Street said.

Medvedev, who currently serves as deputy chair of the Russian Security Council, issued his warning in a social media post.

The British government has pledged £2.5 billion ($3.2 billion) in military aid to Ukraine over the next two years, including in the form of thousands of military drones, which London said will be the largest of their kind ever received by Kiev. Most of the UAVs will be made in the UK, the announcement added.

The UK has been a key supporter of Kiev’s war effort against Russia. Former Prime Minister Boris Johnson reportedly played a significant role in derailing a nascent truce that Kiev and Moscow had negotiated in the early months of the hostilities in 2022, although he has denied ordering the Ukrainian government to keep fighting.

Moscow has on several occasions accused the UK of helping Ukraine organize attacks against Russia, particularly in the Black Sea. The Russian Defense Ministry has claimed that British military personnel already have a presence in Ukraine.