An overnight drone attack on Monday targeted the Engels airbase deep inside Russia for the second time this month, killing three servicemen in what appears to be a renewed sign of Ukraine’s readiness to target offensive threats way beyond its border areas.

Russian Telegram channels reported a strong explosion and a fire, while Russia’s state-run Ria-Novosti news agency, citing the defense ministry, said air defenses downed a Ukrainian drone heading towards the base. Engels air base is located about 600 km northeast of the Ukrainian border.

Delivering a symbolic blow, this second long-range attack on one of Russia’s most strategically important bases — home to nuclear-capable bombers — came on the same day the Russian army was celebrating the 107th anniversary of the creation of its air defense units.

The previous attack happened on December 5.  New York Times has reported that Ukraine carried out the attack with drones and the help of a military reconnaissance unit coordinating it deep inside Russian territory. Russian authorities claimed that attack damaged two planes, killed three servicemen and wounded four others.

On Monday, locals reported a strong blast in the same airfield but the Russian defense ministry claimed no significant damage was done to its aircraft.

Ukraine has not taken responsibility for either strike.

“There is absolutely no threat to residents. Civil infrastructure facilities were not damaged,” Roman Busargin, governor of the Saratov region, said in a statement.

“Law enforcement agencies have been investigating the incident at a military facility.”

Busargin also issued a warning about criminal liability for spreading false information, claiming that news on the incident published in media and by citizens will be promptly sent to law enforcement agencies.

Engels airfield is a base for Russian strategic bombers used to carry missile strikes against Ukraine. In addition, those bombers are also a part of Russia’s nuclear triad, as they can carry nuclear warheads.