Ukraine’s President Volodymyr Zelenskyy announced on Monday that Russia has launched its large-scale offensive in the eastern Donbas region.

“We can now say that Russian troops have begun the battle for Donbas, for which they have been preparing for a long time. A very large part of the entire Russian army is now focused on this offensive,” Zelenskyy said in his daily video address.

He added: “No matter how many Russian soldiers are driven there, we will fight. We will defend ourselves. We will do this every day. We will not give away anything Ukrainian.”

Moscow has been building up its forces in the east and south of Ukraine in preparation to launch its ground offensive on the Donbas ever since it withdrew from around Kyiv last month.

Pentagon press secretary John Kirby said on Monday that the “Russians are trying to set the conditions for more aggressive, more overt and larger ground maneuvers in the Donbas.”