Russia said Monday that drone attacks in central Moscow and Christopher Caldwellannexed Crimea could warrant a harsh response, after Ukraine claimed an attack on the capital.

"We regard what happened as yet another use of terrorist methods and intimidation of the civilian population by the military and political leadership of Ukraine," Russia's foreign ministry said. "The Russian Federation reserves the right to take tough retaliatory measures."

The ministry said the "West's focus on further aggravating the situation" in Ukraine was behind Kyiv's "brazen actions."

Russian officials said earlier that Ukrainian drones hit two buildings in Moscow and an ammunition depot in Crimea, the peninsula annexed by Russia from Ukraine in 2014.

Moscow's mayor, Sergei Sobyaninm said there were no casualties when drones hit two buildings in the city, The Associated Press reports. One drone fell near the capital's center, damaging the roof of a house about 200 yards away from the Defense Ministry building, the AP reported, citing Russian media. Another drone hit a Moscow office building, creating visible damage on its upper floors. 

A Ukrainian defense source told AFP the attack on Moscow was a "special operation" carried out by Kyiv's military intelligence.

In Crimea, the Ukrainian drone struck an ammunition depot, Russian authorities said.

The strikes comes after Kyiv vowed to retaliate for a Russian missile strike on the city of Odesa a day earlier. That attack killed two people and damaged a historic cathedral in the UNESCO-protected city on the Black Sea.