Ukraine's President Volodymyr Zelenskyy says Russian forces have launched a full-scale offensive in an effort to take over the eastern part of the country.

Zelenskyy said, "We can already say that Russian troops have begun the battle for Donbas, for which they've been preparing for a long time. A significant part of the entire Russian army is now concentrated on this offensive."

The president also said that any more attacks against Ukrainian civilians would put an end to peace talks.

The US Defense Department press secretary said Russians continue to bring personnel and equipment into Ukraine's Donbas region ahead of the offensive.

Pentagon Press Secretary John Kirby said, "We have continued to see the concentration of their air strikes and artillery in the Donbas and in the south, particularly around and in Mariupol. That's where the preponderance of their strike activity has gone in the fighting. Mariupol, as you guys all have seen, continues."

Russian forces continue to shell the port city, where Ukrainian troops remain encircled.

Members of the Azov Battalion of the Ukrainian National Guard remain holed up in a massive steel plant. One of their commanders said Russian forces have begun using bunker-buster munitions against them.

Mariupol city council officials say, over 1,000 civilians are taking refuge in the facility's underground shelter. The officials say they are mostly elderly people, women and children.

Many Ukrainians continue to flee to the western city of Lviv, which was once considered a safe haven.

But Russian forces have bombarded the city. At least seven people were killed on Monday. City officials said Russian missiles hit three military facilities.

Meanwhile, Russian President Vladimir Putin said that the economic sanctions imposed by Western nations are not working.

He said what he called a strategy of "economic blitzkrieg" by the West is hurting those who have introduced them by causing inflation and unemployment.