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".
Russia has accused Ukraine of firing drones at the Kremlin in an attempt to kill President Vladimir Putin, and said the United States was behind the purported attack, Reuters reported.
Ukraine has denied that, and the White House has dismissed Russian "lies".
"It was clearly a hostile act, it is clear that the Kyiv terrorists could not have committed it without the knowledge of their masters," Lavrov told a press conference in India.
"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".
