Massive flames and plumes of smoke have lit up the night's sky with a series of enormous blasts reported across various Russian regions close to the Ukraine border in the early hours of Wednesday.
Explosions were heard in the city of Belgorod, said regional governor Vyacheslav Gladkov, and an ammunition depot in the province was on fire.
The province borders Ukraine's Luhansk, Sumy and Kharkiv regions, all of which have seen heavy fighting since Russia invaded Ukraine two months ago.
Gladkov said no civilians had been hurt by the fire which broke out at a facility near Staraya Nelidovka village.
He said on Telegram: "At approximately 03:35 I woke up from a loud bang that sounded like a blast. As I was writing this post, three more blasts were heard.
"According to preliminary information, an ammunition depot is on fire near the village of Staraya Nelidovka.”
Russia this month accused Ukraine of attacking a fuel depot in Belgorod with helicopters and opening fire on several villages in the province.
Suspected attacks from a more assertive Ukraine were also seen in Voronezh and Kursk regions.
Roman Starovoyt, the governor of Russia's Kursk province, which also borders Ukraine, said that explosions had been heard in the city of Kursk early on Wednesday which were most likely the sounds of air defence systems firing.
In Kursk there were unconfirmed reports that Russian air defences had downed Ukrainian military drones.
Explosions were heard in the cities off Kursk and in Oboyan were locals have said they heard military planes flying overhead.
In Voronezh region, there were reports Russian air defences were active to fend off an attack on strategic Baltimore military air base.
Ukraine's general staff said in an update early on Wednesday that Russian forces had captured some settlements in the northeast and the east and a Russian assault on Ukrainian forces holding out in the Azovstal steel plant in the southern city of in Mariupol was still going on.
U.N. Secretary-General Antonio Guterres told Russia's foreign minister on Tuesday that he was ready to fully mobilise the organisation's resources to save lives and evacuate people from Mariupol.
British military intelligence said Ukraine retained control over most of its air space and Russia had failed to effectively destroy Ukraine's air force or its air defences.
Ukrainian authorities on Tuesday dismantled a huge Soviet-era monument in the centre of Kyiv meant to symbolise friendship with Russia, according to the city's mayor.
"We now see what this 'friendship' is - destruction of Ukrainian cities ... killing tens of thousands of peaceful people," Kyiv mayor Vitaly Klitschko said.
It comes as the UK has backed Ukraine if it wants to attack targets on Russian soil.
Defence minister James Heappey said it is “entirely legitimate” for Kyiv’s forces to use western-supplied weapons to launch strikes over the border.
A large fire erupted in the early hours of April 25 at an oil storage facility in the city of Bryansk, 100 miles into Russia over the Ukrainian border.
Foreign Minister Sergei Lavrov claimed the risk of a third world war was “considerable”, saying according to his ministry: “I would not want to elevate those risks artificially. Many would like that. The danger is serious, real. And we must not underestimate it.
"NATO, in essence, is engaged in a war with Russia through a proxy and is arming that proxy. War means war."
Mr Heappey told the BBC that claim was “nonsense and Lavrov knows it”, as weapons have been donated directly by western countries and not by NATO itself.
The UK announced on Monday it will send Stormer armoured vehicles equipped with anti-aircraft rocket launchers to Ukraine.
