Three Russian military personnel have been killed by the falling wreckage of a Ukrainian drone after it was shot down over an air base in the Saratov region, south-east of Moscow, the Russian military says.
"A Ukrainian unmanned aerial vehicle was shot down at low altitude while approaching the Engels military airfield in the Saratov region," a defence ministry spokesperson told reporters.
"As a result ... three Russian servicemen of the technical staff who were at the airfield were fatally wounded."
Earlier on Monday, Ukrainian and Russian media reported that blasts were heard after midnight at the base, home to strategic bombers, hundreds of kilometres from Ukraine's front line.
"There is absolutely no threat to residents. Civil infrastructure facilities were not damaged," Saratov Regional Governor Roman Busargin said.
"Information about the incident at a military facility is being checked by law enforcement agencies."
The RBC-Ukraine news agency reported two explosions, while Russian news outlet Baza cited residents who heard air raid sirens and an explosion.
On December 5, the same air base was struck by what Russia claimed to be one of two Ukrainian drone attacks on local bases.
Analysts said the strikes damaged Moscow's reputation and raised questions about its defence capabilities.
Ukraine has never publicly claimed responsibility for attacks inside Russia, but has said incidents were "karma" for Russia's invasion in February this year.
Russia beefs up missile systems
Russia's defence ministry has told local media its soldiers are working "round-the-clock" to develop new anti-aircraft missile system positions, to defend itself against Ukrainian strikes.
In a statement by the ministry reported by Interfax news agency, crews trained in the use of the S-300V — a Soviet-built device that can track up to 30 kilometres high and 200 kilometres in range — were "mastering new position areas" of the Russian long-range, surface-to-air missile systems.
"The air defence units of the Western Military District continue to serve in the new position areas on combat duty around the clock," a ministry spokesperson said.
The Western Military District is one of five Russian military zones and includes regions that share a border with Ukraine, like Belgorod and Bryansk as well as the Kaliningrad exclave.
The S-300 air defence missile system was originally developed by the Soviet Union, and is being used by both Russia and Ukraine.
In November, a Soviet-made S-300 rocket believed to have been launched by Ukraine, hit Poland killing two people.
Shelling continues across Ukraine
Elsewhere on the battlefield, at least four civilians were wounded by Russian shelling of five regions in Ukraine's south-east over the past 24 hours, according to the deputy head of Ukraine's presidential office, Kyrylo Tymoshenko.
Overall, the intensity of the shelling from Sunday night into Monday was significantly lower.
For the first time in weeks, Russian forces didn't shell the Dnipropetrovsk region, which borders the partially occupied southern regions of Kherson and Zaporizhzhia, its governor, Valentyn Reznichenko, reported on Telegram.
Mr Reznichenko posted it was "the third quiet night in 5.5 months since the Russians started shelling" the areas around the city of Nikopol.
Nikopol is located across the Dnieper River from the Zaporizhzhia nuclear power plant, which is under the control of Russian forces.
Ukrainian-controlled areas of the neighbouring Kherson region had been shelled 33 times over the previous 24 hours, Kherson's Ukrainian Governor Yaroslav Yanushevich said. There were no casualties.
On Sunday, Russian forces attacked the city of Kramatorsk, where Ukrainian forces are headquartered.
Three missiles hit an industrial facility and damaged residential buildings, but no casualties were reported, according to local officials.
In the partially occupied eastern Donetsk region, fierce battles continued around the city of Bakhmut, which Russian forces have been trying to seize for weeks to consolidate their grip on Ukraine's east.
In the neighbouring Luhansk region — which is almost entirely under Moscow's control — Russian forces are "suffering huge losses and medical facilities are overwhelmed with wounded soldiers", Luhansk's Ukrainian governor, Serhiy Haidai, told Ukrainian television on Monday.
The Russian army is redeploying paratroopers from the Kherson region to the area, Mr Haidai said.
He also said that Russian forces have withdrawn from their military command operations post in the town of Kreminna as Ukrainian forces were nearing the town after months of intense fighting.
Russian forces relocated to Kreminna and several other other areas in September after they pulled back from the Kharkiv region in eastern Ukraine.
On Saturday, a deadly attack on the city of Kherson — which was retaken by Kyiv's forces last month — killed and wounded scores of people.
Local residents are lining up to donate blood for the wounded, Mr Yanushevich said on Monday.
ABC/Reuters