Russian Foreign Minister Sergei Lavrov said on Friday that Wednesday's drone incident at the Kremlin was a "hostile act" and Russia would respond with "concrete actions", APA reports citing Reuters.
"We will not respond by talking about 'casus belli' or not, we will respond with concrete actions," he said.
"Casus belli" is a Latin term for an action that provides justification for war. Russia's war in Ukraine is now in its 15th month, though Moscow continues to describe it as a "special military operation".