As Russian troops retreat after losing the key Ukrainian town of Lyman they need to set up a new frontline to protect their dwindling gains -- but one key supply route has already been cut off.
The railway lines in northeastern Ukraine converge at Kupiansk Vuzlovyi before heading south towards Svatove, in the Luhansk region, now claimed by Moscow as an annexed Russian territory.
During the first six months of this year's Russian invasion of Ukraine, the trains rattling through Kupiansk Vuzlovyi's huge marshalling yards carried supplies southwards to the occupation forces.
But now the soldiers patrolling the modern -- but heavily-damaged -- station are Ukrainian and the tracks are silent.
"This site has always been considered a target of strategic importance, it's a railway and cargo connection point," said "Rosomakha", a soldier whose call sign is the Ukrainian word for "Wolverine".
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As Rosomakha's unit visited the station on Sunday, Ukraine's President Volodymyr Zelensky was announcing that Lyman, a frontline town in the Donetsk region, had been cleared of Russian troops.
Kupiansk Vuzlovyi, an industrial suburb on the east bank of the Oskil river southeast of Kupiansk proper, fell a week earlier when the Russian troops holed up in its brick factory withdrew under fire.
The Russian forces are now expected to try again to stall the Ukrainian offensive deeper inside the territory Moscow claims to have annexed, 30 kilometres (19 miles) down the rail line in Svatove.
But Rosomakha and his comrades are not overly concerned. They claim that the Russians fled in disarray and that, once Ukraine has reorganised its forces in Kupiansk, they are ready to press on.
"They escaped in panic and they relocated a lot of units elsewhere in the middle of the summer," he said, adding that recently captured prisoners had given them a good idea of Russian planning.
Ukraine knows, for example, that some of the Russian positions have been reinforced with conscripts since President Vladimir Putin announced what he called a "partial mobilisation" of reserve manpower.
But they are not intimidated by this, nor by Moscow's claim on Friday to have annexed four Ukrainian regions, including Luhansk and Donetsk, into Russia -- a move dismissed by the international community.
"According to Ukrainian law, this is the territory of Ukraine, this is our land," Rosomakha told AFP at Kupiansk Vuzlovyi station, standing by a crater left by a 120mm mortar shell fired by the retreating Russians.
"I'm originally from the Luhansk region, which is why I won't stop until the very last Russian is removed from this land."
Behind him the tall glass windows of the station are shattered, and the ticket hall is empty and silent, the timetable still showing departure times for Kharkiv, Kyiv and the far off Black Sea port of Odessa.