Armen Sarkisyan was accused by Ukraine of aiding Russia's war in Donetsk. A pro-Putin paramilitary leader was killed in a bomb blast in the lobby of a luxury apartment building in Moscow, according to Russian authorities and news reports. Armen Sarkisyan, who Ukraine has accused of aiding Russia's war in Donetsk, was targeted in the attack; he was critically injured in the blast and later died in hospital, according to the Kommersant newspaper.

Another person was killed and three others injured in the blast. State news agency Tass cited an unidentified law enforcement source as saying a bomb was planted in the building. In December, Sarkisyan – who also ran a boxing federation – was charged in absentia by the Security Service of Ukraine with participation in illegal armed or paramilitary formations or assisting such formations in combat operations against its armed forces.

The agency, known as the SBU, has previously accused Sarkisyan of recruiting prisoners to fight in Ukraine, cooperating with Russian security forces, and creating an armed formation known as “ArBAT” – or “Armenian Battalion”. The ArBAT group fought the Ukrainian army in the Toretsk area of the Donetsk region, as well as in Russia's Kursk region, the SBU said. Ukrainian forces launched an incursion in the Kursk region in August.

Meanwhile, Ukrainian long-range drones struck one of Russia's biggest oil refineries for the second time in three days, a senior Kyiv official said. The attack, late on Sunday, hit a refinery in the Volgograd region, which is one of Russia's 10 biggest refining facilities, processing close to 6% of the country's oil, an official in Ukraine's security service told The Associated Press. Russian authorities acknowledged only a brief fire at the Volgograd refinery during the drone attack.

Ukrainian defences are creaking under a months-long Russian drive to occupy more land, especially in Ukraine's eastern industrial heartland, before the possible start of peace negotiations steered by US president Donald Trump. Though heavily dependent on Western military aid, Ukraine has been developing its own arms industry, including drones that can fly increasingly long ranges with bigger payloads.

Also on Monday, the father of an 18-year-old British volunteer who was killed by a Russian drone while on his first mission fighting in Ukraine has paid tribute, saying his son was a "polite, likeable young man". James Wilton, from Huddersfield, West Yorkshire, left college and travelled to join international fighters, against the wishes of his mother and sisters, because he wanted to make a difference and to help those suffering from the war.

He was killed in July in a drone attack when crossing open ground with a heavy pack on his back and could not be saved, despite the efforts of his friend, an American volunteer named Jason. Mr Wilton's father Graham said: “My son James had only just turned 18 when he decided he wanted to go volunteer and fight in Ukraine. “I didn't necessarily agree with his decision on this but we talked at length about why he wanted to do this. He'd just finished college and wasn't really sure about what he wanted from life.

“But from our conversations he made it clear to me that this was what he wanted to do. So I did everything I possibly could to make sure he knew exactly what was involved and that he could be fully prepared for what may lay ahead.”. Mr Wilton said his son spent three months in Ukraine where he received combat training, and he described them as “some of the best days of his life”. “Unfortunately it was not to be and I guess you can never fully prepare for what happens on the battlefield. I thank Jason for his bravery in trying to save James in a bad moment and for getting him off the battlefield, even if it was in vain.”.