A blast hit an airbase inside Russia on Tuesday, the latest in a series of apparent Ukrainian drone attacks that showcase an ability to strike at the heart of Russian territory and suggest a new boldness in Kyiv's fight against Moscow's war.
An airfield at Kursk in southwest Russia, near the Ukrainian border, was ablaze on Tuesday morning, with regional governor Roman Starovoit saying the incident was the result of a drone attack.
Photos and video verified by NBC News showed a large fire at the airfield caused by a suspected damaged oil tanker, with smoke trailing miles across the sky.
Similar explosions were seen on Monday at the Engels air base outside the city of Saratov and at Ryazan, just 125 miles southwest of Moscow and hundreds of miles away from the Ukrainian border.
The Engels base houses Russia's strategic bombing fleet of tu-160 and tu-95 planes, which have been used on long-range bombing missions to Ukraine and can be adapted to carry nuclear weapons.
Ukraine has not directly claimed responsibility, but officials have jokingly suggested its military may be behind the incidents. Russia's defense ministry blamed Kyiv's forces for the two blasts Monday, in which it said three "maintenance personnel" died and two planes were damaged.
Analysts were cautious about the military impact of the apparent attacks on strategic sites far from the front lines, but said they had further undermined Russian confidence in the country's air defenses while providing a timely morale boost for Ukrainian civilians preparing for a long winter under bombardment.
"The signaling is important for the Ukrainians: They need to know that they are hitting back, given the amount of pain and devastation and general discomfort that's being meted out in Ukraine," Matthew Ford, an associate professor at the Swedish Defense University in Stockholm, told NBC News.
"It's important from a morale point of view that some Russian strategic resources are being targeted."
Russia has the firepower to carry on bombing Ukraine, he added. "It might be a pain, but they can relocate aircraft and infrastructure, they can put up more security around air bases."
The attacks were inflicted, the Kremlin said, by "Soviet-made UAV," or unmanned aerial vehicles. This suggests Ukraine is not using the billions of dollars' worth of lethal aid it has received from the United States and other Western allies in attacks on Russian soil, which Washington has feared could trigger an escalation.
As with the Ukrainian liberation of Kherson from Russian forces, this week's drone attacks have been received badly by some commentators and military bloggers inside Russia, who have demanded retaliation for what they see as a serious reputational blow.
The Institute for the Study of War, a U.S.-based military think tank, said the drone attacks had inflicted "light damage while demonstrating Ukraine's ability to strike Russian rear areas and possibly disrupt Russia's campaign of strikes against Ukrainian infrastructure."
"If Russia assesses the incidents were deliberate attacks, it will probably consider them as some of the most strategically significant failures of force protection since its invasion of Ukraine," the British Ministry of Defense said in its daily intelligence update on the war Tuesday.
The apparent drone attacks come after cities across Ukraine have been hit by a sustained bombing campaign, with repeated damage to energy infrastructure leaving millions without heat or power.
"Engels is the main operating base of Russia's Long Range Aviation (LRA) within western Russia and is home to more than 30 heavy bombers," the U.K. ministry said.
"These aircraft contribute to Russia's nuclear deterrent and have also frequently been used to launch conventional cruise missiles at Ukraine. The LRA is likely to respond by temporarily moving bombers to dispersal airfields."
Ukraine has launched occasional attacks into Russian-held territory and into Russia itself since the war began on Feb. 24. In August the Saki airfield in Crimea was hit, while a huge explosion destroyed a key bridge linking Russia and the annexed peninsula in October.
President Vladimir Putin drove across the rebuilt bridge in a Mercedes on Monday, in a scene broadcast on Russian state TV that was seemingly aimed at fixing some of the reputational damage inflicted by the blast.
Kremlin spokesman Dmitry Peskov said in his daily press briefing Tuesday that the claimed Ukrainian attacks were "terrorist acts" and said "necessary measures" would be taken to protect key facilities.
Ukraine has liberated more than half of the land Russia has seized since the start of the war, the British MOD said Monday, leaving Russia in control of about 18% of Ukraine.
This article was originally published on NBCNews.com