Photographs on the Facebook page of an army unit showed Zelensky at a ceremony in the main square to raise the Ukrainian flag over the city’s administrative building. Hanna Maliar, the Deputy Minister of Defense, was also present.
“Earlier, when we looked up, we always looked for the blue sky. Today, when we look up, we are looking for only one thing – the flag of Ukraine,” Zelensky said in a post on the presidential Telegram channel.
“Our blue-yellow flag is already flying in the de-occupied Izium. And it will be so in every Ukrainian city and village. We are moving in only one direction – forward and towards victory.
“I want to thank you for saving our people, our hearts, children and future,” Zelensky said, according to a statement released on the presidential website.
“It has been extremely difficult for you in recent months. Therefore, I ask you to take care of yourselves, because you are the most valuable asset we have,” he said.
“It may be possible to temporarily occupy the territories of our state. But it is definitely impossible to occupy our people, the Ukrainian people,” he said.
There was a minute’s silence at the ceremony to remember those who had been lost during military operations.
Ukrainian forces took back control of Izium on Saturday, marking a huge strategic blow to Russia’s military assault in the east.
The city, which sits near the border between the Kharkiv and Donetsk regions, was under Russian occupation for over five months and became an important hub for the invading military. Moscow was using Izium as a launching pad for attacks southward into the Donetsk region and Kupyansk, some 30 miles to the north of Izium, as a rail hub to resupply its forces.
Zelensky told journalists he was “shocked” by the number of “destroyed buildings” and “killed people” left in the wake of the Russian occupation.
“Unfortunately, this is part of our history today. And this is part of the modern Russian nation – what they did,” he said.
He also thanked foreign governments for sending investigators and prosecutors to investigate alleged human rights abuses by occupying forces in Ukraine, adding that all occupied areas would eventually return.
“We should send signals to our people who, unfortunately, are still under occupation. And my signal to the people in Crimea: we know that these are our people, and it is a terrible tragedy that they have been under occupation for more than eight years. We will return there. I don’t know when exactly. But we have plans.”
In a sign that Kyiv’s sustained military offensive is working, Zelensky said on Tuesday that 8,000 square kilometers (3,088 square miles) of territory has now been liberated by Ukrainian forces so far this month, with roughly half the area still undergoing “stabilization” measures.
On Monday, the President said that most of the territory regained by Ukrainian forces since the start of September was concentrated in the country’s northeastern and southern regions.
CNN’s Ivana Kottasová, Tim Lister, Yulia Kesaieva, Denis Lapin, Josh Pennington and Victoria Butenko contributed reporting to this story.