The first explosion hit a tanker train in the Severonomuisky tunnel in Buryatia early Thursday, causing a fire that took hours to extinguish, Russian news outlets said. The 15.3-kilometre (9.5-mile) tunnel in southern Siberia is the longest in Russia.

A second explosion hours later hit another train carrying fuel as it crossed a 35-metre (115-foot) high bridge across a deep gorge while travelling on a bypass route, according to the Ukrainian news reports.

Russian Railways, the state company that operates the vast rail network, said traffic had been diverted along a new route after the first attack, slightly increasing journey times but not interrupting transport.

It also confirmed the tunnel explosion but did not say what caused it.

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Russian daily business newspaper Kommersant cited investigators saying an explosive device was planted under one of the train’s carriages.

There was no comment from Russian authorities on the second explosion.

A Ukrainian source said the second attack had anticipated the diversion of rail traffic and targeted the backup route at Chertov Bridge.

A Russian industry source, who declined to be identified, said the backup route was functioning and being used by trains carrying freight on Friday afternoon.

Ukrainian authorities have emphasised that the country’s military and security agencies can strike targets anywhere in Russia to fight Moscow’s aggression.

Officials in Kyiv have claimed responsibility for some previous attacks on infrastructure facilities deep inside Russia.

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Ukraine says Russian strike killed over 50 in one of the deadliest attacks of the war

Ukraine says Russian strike killed over 50 in one of the deadliest attacks of the war

Russia’s top counter-intelligence agency, the Federal Security Service, or FSB, said on Friday that it detained a man accused of attacking a military airbase in western Russia with exploding drones in July and staging an explosion that derailed a cargo train in western Russia last month.

The FSB identified the suspect as a dual Russian-Italian citizen and alleged he was recruited by the Ukrainian military intelligence in Istanbul and underwent training in Latvia before returning to Russia.

There was no immediate comment on the claim from Ukrainian authorities.

As the war continued into its 22nd month, Ukraine’s forces shot down 18 of 25 Iranian-made Shahed exploding drones and one of two air-launched missiles that Russia launched early Friday, the Ukrainian air force said.

The office of Ukrainian President Volodymyr Zelensky reported that Russian strikes across Ukraine killed at least four civilians and wounded 16 others between Thursday and Friday mornings.

Three of them died when Russian warplanes struck the village of Sadove in southern Ukraine’s Kherson region; the fourth was killed in Russian shelling of the town of Toretsk in the eastern Donetsk region, the presidential office said.

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Zelensky also said that changes were needed to improve Ukraine’s system of mobilisation as part of an overall strategy to improve the country’s military position in the war.

He said a meeting of the military command had discussed scenarios to produce “concrete results” for 2024 in conditions of war. “In particular, this concerns the issue of mobilisation. Everyone in Ukraine understands that changes are needed in this domain,” Zelensky said.

“This is not simply a question of numbers, of who can be mobilised,” he said. “It’s a question of a time frame for each person who is now in the military, for demobilisation and for those who will join the military. And it’s about conditions.”

Zelensky said the issues had to be examined by commanders and the defence ministry.

Additional reporting by Reuters