WATCH: State Department holds briefing following alleged Ukraine drone strikes inside Russia

State Department spokesman Ned Price held a briefing Tuesday afternoon after drones struck inside Russia’s border with Ukraine in the second day of attacks.

Watch the briefing in the player above.

The attacks exposed the vulnerability of some of Moscow’s important military sites, observers said.

Ukrainian officials did not formally confirm carrying out drone strikes inside Russia, and they have maintained ambiguity over previous high-profile attacks. But Ukrainian presidential adviser Mikhail Podolyak taunted Moscow in comments on Twitter.

WATCH: Western nations cap price of Russian oil over war in Ukraine

Britain’s Defense Ministry said Russia was likely to consider the attacks on Russian bases more than 500 kilometers (300 miles) from the border with Ukraine as “some of the most strategically significant failures of force protection since its invasion of Ukraine.”