KYIV: A drone believed to be Ukrainian penetrated hundreds of kilometers through Russian airspace, causing a deadly explosion at the main base for Moscow’s strategic bombers in the latest attack to expose gaps in its air defences.

Moscow said it had shot the drone down causing it to crash at the Engels air base, where three service members were killed. Under its usual policy on incidents inside Russia, Ukraine did not comment. The base, the main airfield for the bombers that Kyiv says Moscow has used in recent months to attack Ukrainian civilian infrastructure, is hundreds of miles from the Ukrainian frontier. The same planes are also designed to launch nuclear-capable missiles as part of Russia’s long-term strategic deterrent.

A suspected drone already struck it on Dec. 5, exposing what was widely described at the time as a humiliating hole in Russia’s air defences that the latest attack suggests Moscow has yet to plug.

The Russian defence ministry said in a statement no planes were damaged, but Russian and Ukrainian social media accounts said several had been destroyed. Reuters was not able to independently verify the reports.

As the war entered its 11th month, Russian President Vladimir Putin hosted leaders of other former Soviet states in St Petersburg on Monday for a summit of the Commonwealth of Independent States group, which Ukraine has long since quit.