Medvedev, who is deputy chairman of Russia's Security Council, said such steps by the West were bringing World War Three closer, Reuters reported.
In a post on Telegram, Medvedev first directed his ire towards recently appointed British Defense Minister Grant Shapps, who said in a newspaper interview that London wants to deploy military instructors to Ukraine, in addition to training Ukrainian armed forces in Britain or other Western countries as at present.
"(This will) turn their instructors into a legal target for our armed forces," Medvedev wrote on Telegram. "Understanding perfectly well that they will be ruthlessly destroyed. And not as mercenaries, but namely as British NATO specialists."
Medvedev then turned his focus to Germany, vilifying those who want Berlin to supply Ukraine with Taurus cruise missiles that could strike Russian territory and try to limit Moscow's supply to its army.
"They say this is in accordance with international law. Well, in that case, strikes on German factories where these missiles are made would also be in full compliance with international law," Medvedev said.
"These morons are actively pushing us towards World War Three," he added.