Here's a quick summary of where Russian troops have advanced in Ukraine in the last few hours
Fighting has broken out on the streets of Kharkiv, Ukraine's second-largest city, after Russian forces entered the city.
The Russian Ministry of Defense has previously said it was targeting only military infrastructure, saying in a statement: “The Armed Forces of the Russian Federation do not strike cities and towns, they take all measures to save the lives of civilians.”
But Zelensky said Sunday: “They lied when they said they would not target civilian population. Since the first hours of the invasion, Russian troops have been hitting civilian infrastructure.”
“This is terror,” he added, while Ukrainian Prime Minister Denys Shmyhal said Russia was committing "war crimes."
Meanwhile, the commander of Ukrainian forces in Kharkiv, Oleg Synegubov, has claimed that dozens of Russian troops have surrendered amid continued fighting in the city, which is some 20 miles from the Russian border.
Battles have also raged in the capital of Kyiv and the southern city of Kherson in recent days.
But Russian forces have been unable to capture any of Ukraine's major cities since launching their invasion on Thursday.
Russia is encountering "stiffer than expected" resistance from the Ukrainian military as well as unexpected difficulties supplying its forces, two senior US officials with direct knowledge tell CNN.
On the battlefield, Russia is suffering heavier losses in personnel and armor and aircraft than expected. This is due in part to the fact that Ukrainian air defenses have performed better than pre-invasion US intelligence assessments had anticipated.
In addition, Russia has yet to establish air supremacy over Ukraine, a senior defense official said, as the Ukrainian Air Force and air defense systems fight for control of the airspace.