Ukraine fired missiles and drones at factories and energy facilities across Russia early on Tuesday, sparking fires hundreds of kilometres (miles) from the frontline, a source in Ukraine's SBU security services said.

The Russian military accused Kyiv of using US- and British-supplied missiles and promised the strikes would "not go unanswered".

The barrage forced schools in the southwestern Saratov region to close, while at least nine airports in central and western Russia temporarily halted traffic, according to Russian officials.

Moscow and Kyiv have upped strikes on one another ahead of US President-elect Donald Trump's inauguration next week, as both sides seek to gain the upper hand in potential negotiations aimed at settling the nearly three-year war.

There were explosions at "chemical plants, oil refineries and warehouses" in Russia overnight, a source in Ukraine's SBU security services told AFP, saying Kyiv had hit "Russian military-industrial complex" sites.

Among the targets hit early on Tuesday were chemical plants in the western regions of Tula and Bryansk, the........

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