Any attempt to arrest President Vladimir Putin after the International Criminal Court (ICC) issued a warrant for the Kremlin chief would amount to a declaration of war against Russia, his ally Dmitry Medvedev said on Thursday.

The ICC issued an arrest warrant on Friday, accusing Putin of the war crime of illegally deporting hundreds of children from Ukraine. It said there are reasonable grounds to believe that Putin bears individual criminal responsibility.Former President Dmitry Medvedev told Russian media that the ICC, which countries including Russia, China and the United States do not recognise, was a “legal nonentity” that had never done anything significant.

Any attempt to detain Putin, though, would be a declaration of war, said Medvedev, who serves as deputy chairman of Putin’s powerful security council.

“Let’s imagine – obviously this situation which will never be realised – but nevertheless lets imagine that it was realised: The current head of the nuclear state went to a territory, say Germany, and was arrested,” Medvedev said.

“What would that be? It would be a declaration of war on the Russian Federation,” he said in a video posted on Telegram. “And in that case, all our assets – all our missiles et cetera – would fly to the Bundestag, to the Chancellor’s office.”

The Kremlin says the ICC arrest warrant is an outrageously partisan decision, but meaningless with respect to Russia. Russian officials deny war crimes in Ukraine and say the West has ignored what it says are Ukrainian war crimes.

Russia’s Feb. 24 invasion of Ukraine has triggered the deadliest European conflict since World War Two and the biggest confrontation between Moscow and the West since the 1962 Cuban Missile Crisis.

Relations with the West, Medvedev said, were probably at the worst point ever.As president from 2008 to 2012, Medvedev cast himself as a pro-Western reformer. Since the war, though, he has turned into one of the most publicly hawkish Russian officials, insulting Western leaders and delivering a series of nuclear warnings.