"Let's imagine - it's clear that this is a situation that will never happen - but nevertheless let's imagine it does," Putin ally Dmitry Medvedev said.
"The current head of a nuclear state arrives on the territory of, say, Germany, and is arrested. What is this? A declaration of war against the Russian Federation."
Medvedev said that if this happened "all of our means, rockets and others, will fly on the Bundestag, in the Chancellor's Office and so on."
Medvedev, deputy chairman of Russia's security council, said the ICC's decision will make dire relations with the West plunge further.
His comments came two days after Russia opened a criminal investigation into ICC prosecutor Karim Khan and several other ICC judges, saying their decision was "unlawful".
The Hague-based court had also issued a warrant against Maria Lvova-Belova, Russia's presidential commissioner for children's rights.
On Wednesday, the ICC's legislative body said it regretted "threats" against the tribunal over its warrant.
"The presidency of the assembly regrets these attempts to hinder international efforts to ensure accountability for acts that are prohibited under general international law," it said in a statement.
Medvedev Claims Putin ICC Arrest 'Declaration of War'
FILE: Ukrainian Prosecutor General Kostin (left) and ICC Prosecutor Khan (right) and visit the site of a residential building damaged by a Russian missile strike in Vyshhorod, Ukraine. Taken Feb. 28, 2023. Putin's ICC charges stem from the taking of Ukraine children by Russia.
MOSCOW - Russia ex-president Dmitry Medvedev warns that attempts to arrest Vladimir Putin abroad after the International Criminal Court (ICC) issued a warrant against him would be seen by Moscow as a "declaration of war."