Gaiday dismissed claims by pro-Russian separatists fighting alongside Moscow's forces who claim to control half of the city situated across the river from neighbouring Severodonetsk, which was captured by the Russian army last week.
He said that the shelling on Lysychansk was "very powerful... meaning it is no longer possible to evacuate" the remaining 15,000 civilians still in the city, which had a population of around 100,000 before the war.
"It's very dangerous," he said, pointing out that the city's geographical position nevertheless made it easier to defend than Severodonetsk.
"We can simply say that the Russians are very numerous and are arriving from all sides. There's an incredible number of vehicles and artillery."
Lysychansk is the last major city the Russians need to take over in the Lugansk region, one of two provinces in the large Donbas region that Moscow wants to control completely.
