Medvedev wrote about this on Telegram.
He made the statement while commenting on the words of British Foreign Secretary James Cleverly.
Cleverly said that Ukraine, in defence, has the right to use force outside its borders to undermine Russia's ability to direct forces at Ukraine itself.
Medvedev said that the UK "within the framework of generally recognised international law governing the conduct of modern warfare" can be qualified as a state at war with Russia.
"Today, the UK acts as an ally of Ukraine, providing it with military assistance in the form of equipment and specialists, i.e., de facto waging an undeclared war against Russia. In this case, any of its officials (both military and civilian) who contribute to the war can be considered a legitimate military target," Medvedev wrote.
Russian former president Dmitry Medvedev reacted to the words of US Republican Senator Lindsey Graham about the "best use of money" in the form of, as he put it, helping Ukraine physically neutralise the Russian occupiers.