Three people have died after a strategic airbase housing Vladimir Putin 's nuclear bomber planes was hit by a Ukrainian drone.
Loud blasts were heard early on Monday at the airfield deep inside Russia, which is used by the military's Tu-95 and Tu-160 nuclear missile-carrying planes.
Early reports said three people were killed and four more hospitalised following the attack on the Engels-2 military base in the Saratov region, according to Russian news outlet Baza.
No nuclear material is thought to have been involved in the explosion.
The blast is believed to have been the latest long-range kamikaze drone attack on the base by Volodymyr Zelensky 's forces, with the nearest Ukrainian settlement located about 450 miles away.
The "incident" at the air base hundreds of kilometres from the front line of the war in Ukraine.
Video footage showed bright flashes around the base as air raid sirens sounded throughout the area, with the sound of gunfire also heard.
Russia's defence ministry says its air defences shot down the Ukrainian drone flying at low altitude at about 01:35 local time on Monday (22:35 GMT Sunday).
Three Russian servicemen died of injuries caused by drone debris, it adds.
Saratov governor Roman Busargin expressed his condolences to the men's families and friends and said there was "absolutely no threat to residents" in the town of Engels itself.
He added that "all stories about the evacuation from the city are blatant lies" created by people outside Russia, and warned citizens not to give details about the incident online or face possible prosecution.
Earlier this month Russia accused Ukraine of a similar attack on the airfield, home to strategic bombers.
Kyiv has never publicly claimed responsibility for attacks inside Russia and Ukrainian officials have described such incidents as "karma" for Russia's invasion.
A local said on Monday: "When it hit for the first time (December 5), the sound of the explosion was stronger.
“I thought someone's gas had exploded, I ran out into the street, and all the car alarms went off in the area, although I live about two kilometres away from the airfield.
“Today at about 2:30 am local time I heard a whistle and then a loud "clap" - not one car alarm went off.
“The whistle before the ‘pop’ was distinct.”
Russian military blogger Boris Rozhin said: “According to preliminary information, a projectile tried to drop a drone on the airfield.
“Local residents report explosions. Air defences went off.”
