Ukrainian forces have recaptured a key city and inflicted heavy losses on the Russian army, according to defence officials.
Lieutenant General Serhiy Shaptala said the defending forces had seized Chuhuiv from Russian control and killed large numbers of Putin's men.
Two high-ranking Russian commanders were killed in the battle.
The General Staff said on Facebook: "In the course of hostilities, the city of Chuhuiv was liberated.
"The occupiers suffered heavy losses in personnel and equipment.
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"Lieutenant Colonel Dmitry Safronov, Commander of the 61st Separate Marine Brigade of the Russian Armed Forces, and Lieutenant Colonel Denis Glebov, Deputy Commander of the 11th Separate Airborne Assault Brigade of the Russian Armed Forces, were killed."
Chuhuiv, a town of about 30,000 people in the north east of Ukraine, was one of the first to be overrun by the Russians.
An apartment block in the city was shelled heavily a week ago, leading to the death of a young boy.
A woman was also caught up and injured in the blast, with a photo of her bandaged and heavily bleeding face becoming one of the enduring images of the war so far.
Lieutenant Shaptala also gave an update on the number of losses suffered by the invading forces - numbers far higher than those offered by the Russians last week.
He said that more than 11,000 Russian soldiers had died and 290 tanks destroyed in the course of the invasion.
Forty-six planes and 68 helicopters had been downed, the army chief said.
So far the Ukrainian resistance forces have mostly foiled Russian plans to overwhelm the defences of the country's major cities.
The biggest prize the Russians have claimed so far is the city of Kherson, which fell into their hands four days ago.
In a show of defiance, people living in the city ignored orders from the invading forces to protest in the streets on Saturday.
Lieutenant Shaptala has said that the intensity of fighting eased on Sunday, but only while the Russians regrouped ahead of predicted offensive strikes on Kyiv and Kharkiv.
"Our greatest advantage over the enemy is in the zgurtovanost (cohesion) of Ukrainian society," Lieutenant Shaptala said.
"In Russia they do not understand what is self-organization and what is real trust between power and citizens.
"They have been destroying people's freedom and dignity for decades to gain a submissive population."
