Russia said on Monday that three of its military personnel were killed in what it said were Ukrainian drone attacks on two Russian air bases hundreds of miles from the front lines in Ukraine.

Iran PressEurope: Ukraine did not directly claim responsibility. If it did carry out the attacks, they were the deepest military strikes it has conducted inside the Russian heartland since Moscow invaded on Feb. 24.

One of the targets, the Engels air base near the city of Saratov, houses bomber planes that are part of Russia's strategic nuclear forces.

One of the targets, the Engels air base near the city of Saratov, houses bomber planes that are part of Russia’s strategic nuclear forces.

“The Kyiv regime, in order to disable Russian long-range aircraft, made attempts to strike with Soviet-made unmanned jet aerial vehicles at the military airfields Dyagilevo, in the Ryazan region, and Engels, in the Saratov region,” the Russian defense ministry said.

The ministry called it a “terrorist act” aimed at disrupting its long-range aviation.

Despite that, it said, Russia responded with a “massive strike on the military control system and related objects of the defenses complex, communication centers, energy and military units of Ukraine with high-precision air- and sea-based weapons” in which it said all 17 designated targets were hit.

Ukraine said it shot down more than 60 of over 70 missiles launched by Russia on Monday - the latest in weeks of attacks targeting its critical infrastructure that have cut off power, heat and water to many parts of the country.