Russian forces are shelling and attacking Ukrainian positions on the front lines of the conflict around the clock, Ukrainian President Volodymyr Zelenskyy said on Monday.

"Enemy shelling and attacks are occurring round the clock," Zelenskiy said in his nightly video message.

"But the battle for Donbas goes on. And the battle for the south goes on. We see how Russia is massing its forces and we know how to respond."