Ukrainian military officials warned Friday that Russia is looking to "replenish" its personnel by conscripting Ukrainian men in southern regions, amid reports of heavy Russian losses. 

"To replenish their personnel there have been preparations for so-called mobilization in Kherson and Zaporizhzhia oblast," Ukraine’s Ministry of Defense spokesman Colonel Oleksandr Motuzyanyk told reporters. "Russian troops are blocking local people from leaving occupied territories in particular, those males of conscript age."

Fighters of the Chechen special forces unit walk in a courtyard in Mariupol, Ukraine, on Thursday, April 21.

Fighters of the Chechen special forces unit walk in a courtyard in Mariupol, Ukraine, on Thursday, April 21. (REUTERS/Chingis Kondarov)

UKRAINE DISPUTES RUSSIA'S CLAIM THAT IT WILL NOT STORM MARIUPOL STEEL PLANT FULL OF CIVILIANS

It remains unclear how many Russian soldiers have been killed in the last 58 days of fighting and Moscow has refrained from updating its causality figures in four weeks.

Ukraine’s Ministry of Foreign Affairs claimed Friday that more than 21,000 Russian troops have been killed in the last eight weeks, though these figures have not been verified. 

In late March, the Kremlin claimed it had lost 1,350 military personnel since the war began, but a NATO official alleged those figures were likely closer to between 7,000 and 15,000 deaths. Ukraine at the time had claimed there were more than 18,000 Russian losses.

A convoy of pro-Russian troops moves along a road in Mariupol, Ukraine, on Thursday, April 21.

A convoy of pro-Russian troops moves along a road in Mariupol, Ukraine, on Thursday, April 21. (REUTERS/Chingis Kondarov)

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The colonel’s comments came just hours after a Russian general announced that Moscow’s aim was to establish "full control" of not only the eastern Donbas area but southern regions that run along the Black Sea. 

Motuzyanyk said Russia was now looking to annex the regions of Zaporizhzhia, which neighbors Donbas, and Kherson, which sits just north of Russian-occupied Crimea. 

"The Russian occupiers have been using the tactics of terrorizing Ukrainian citizens," he said. "There are still killings, torture, persecution of the local governments."

Adding that Russia is still "blocking evacuation routes and humanitarian aid routes." 

"The enemy is preparing for [a] so-called referendum for occupied territories in Kherson and Zaporizhzhia to join the Russian Federation," he added

Ukrainian President Volodymyr Zelensky warned he would not tolerate the annexation of any part of Ukraine. 

Ukrainian President Volodymyr Zelenskyy in Kyiv

Ukrainian President Volodymyr Zelenskyy speaks from Kyiv, Ukraine, on Tuesday. (Ukrainian Presidential Press Office via AP)

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"I want to say straight away: any ‘Kherson People's Republics’ are not going to fly. If someone wants a new annexation, it can only lead to new powerful sanctions strikes on Russia," he said.

"You will make your country as poor as Russia hasn’t been since the 1917 civil war. So it is better to seek peace now," Zelenskyy added.