LVIV, March 31 - President Volodymyr Zelenskiy on Thursday said the situation in the south and the Donbas region remained extremely difficult and reiterated that Russia was building up forces near the besieged city of Mariupol, Reuters reported.

And in a rare sign of internal dissent, Zelenskiy also said in a video address that he had sacked two senior members of the national security service on the grounds they were traitors.

Zelenskiy, who often uses colorful imagery, said the Russians were so evil and so keen on destruction that they seemed to be from another world, "monsters who burn and plunder, who attack and are bent on murder".

Russia says it is carrying out a "special operation" to disarm and "denazify" its neighbor. Moscow also denies Kyiv's accusations that Russian forces are targeting civilians.

Zelenskiy said Ukrainian forces had pushed back the Russians from Kyiv and Chernihiv - two cities Moscow had announced would no longer be the focus of attacks as they seek to secure the separatist Donbas and Luhansk regions in the south-east.

"There will be battles ahead. We still need to go down a very difficult path to get everything we want," he said.

"The situation in the south and in the Donbas remains extremely difficult." (rt/ez)