According to Ukrainian President Volodymr Zelenskiy and leading authorities, Russian troops carried out a new attack throughout most of Ukraine's eastern border on Monday, and the "Battle of Donbas" has already commenced.

After Moscow moved its soldiers from between Kyiv and Ukraine's north early last month to concentrate on an assault on the Ukrainian territory of Donbas, Ukraine's forces have been ready for a new Russian attack on its eastern border.

In a video speech, Zelenskiy said that they can now claim that Russian troops have begun the assault on the said place, for which they have long planned.

"They (Russian soldiers) started their attempt to launch the advanced stage this morning," Ukraine Defense Council Secretary Oleksiy Danilov stated on television.

He added that this morning, the invaders attempted to breach through the fortifications along practically the whole front barrier of the eastern Luhansk, Donetsk, and Kharkiv areas.

Russia has been strengthening its military in Ukraine's east with troops it has withdrawn from Ukraine's north and Belarus, a key Russian supporter.

The Ukrainian current military administration claimed on Facebook that Russia's main combat unit was concentrating on gaining power in the whole Donetsk and Luhansk areas, which make up the Donbas stretch of land.

Andriy Yermak, the Ukrainian president's commander-in-chief, stated on Telegram that the second stage of the fight has started and to continuously believe in Ukraine's military.

Russian forces have set the stage for a long conflict that military specialists predict will result in severe casualties on both sides as the Russians aim to surround Ukraine's fighters defending the Donbas region.

Major Serhiy Volyna, the leader of a marine battalion in Mariupol, wrote an open letter to Pope Francis yesterday, pleading with him to assist in the evacuation of vulnerable residents from the Avozstal plant, which he said were residing there with his troops.

Mariupol mayor Vadym Boichenko told Ukrainian television on Monday that they have confirmed through the municipal record that they have already evacuated over 40,000 people. 

"I'm sure you've seen a lot in your life. However, I am confident that you have never witnessed the events in Mariupol. Because just what hell appears like on Earth," he wrote.

A senior United States defense source said on Monday that the U.S. military plans to begin preparing Ukrainians on how to use howitzer weapons in the following days.