KYIV, Ukraine (AP) — Drones struck inside Russia's border with Ukraine on Tuesday in the second day of attacks exposing the vulnerability of some of Moscow's most important military sites, experts said.

Ukrainian officials did not formally confirm carrying out drone strikes inside Russia, and they have maintained ambiguity over previous high-profile attacks.

But 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 si...