Ukraine's president has visited the country's eastern frontline amid an escalation of tensions with neighbouring Russia that has raised fears of a resumption of large-scale hostilities.
In Moscow, a senior Kremlin official sternly warned Ukraine against using force to reclaim control of the rebel east, saying that this might force Russia to step in to protect civilians there.
The conflict with Russia-backed separatists in eastern Ukraine erupted shortly after Moscow's 2014 annexation of Ukraine's Crimea peninsula. More than 14,000 people have died in the fighting.
Officials in Ukraine and the West have raised concerns about increasingly frequent ceasefire violations in the country's industrial heartland, known as Donbas.
They also accused Russia of sending troops and weapons along the border to support the rebels there – accusations the Kremlin has denied.
And after tweeting that he wanted to "be with our soldiers in the tough times in Donbas," the Ukrainian president, Volodymyr Zelenskiy, arrived in the heart of the conflict area on Thursday.
He said a 23-year-old Ukrainian soldier had been killed in the area on Wednesday night.
He told troops: "Thank you for keeping people calm and defending our land. You are a true example of heroism and dedication. We remember every warrior who died defending our state."