The main tasks of the first stage of Russia's special military operation in Ukraine have been completed in general, the Russian military said Friday.

"The combat potential of the Ukrainian Armed Forces has been significantly reduced," said Sergei Rudskoy, first deputy chief of the General Staff of the Russian Armed Forces.

"Our forces and means will concentrate on the main thing -- the complete liberation of Donbass," he said.

The Ukrainian cities of Kiev, Kharkov, Chernihiv, Sumy and Nikolaev are blocked by Russian troops, while Kherson and most of the Zaporozhye region are under Russia's full control, Rudskoy said.

Since the start of the military operation a month ago, more than 14,000 Ukrainian troops have been killed and about 16,000 others wounded, said Rudskoy.

"The Ukrainian air forces and air defense systems have been almost completely destroyed. The country's naval forces have ceased to exist," Rudskoy told reporters.

As for the Russian side, 1,351 servicemen have been killed and 3,825 others injured, he said.

"I want to emphasize that the special military operation is being carried out strictly according to the approved plan," Russian Defense Ministry spokesman Igor Konashenkov said.