(NewsNation) — As the war in Ukraine marked 200 days on Sunday, the country has reclaimed broad swaths of the north and east in a long-anticipated counteroffensive that has dealt a heavy blow to Russia — which was also its largest counteroffensive to date.

The counterattack began in the final days of August and at first focused on the southern region of Kherson, which was swept by Russian forces in the opening days of the invasion. But just as Moscow redirected attention and troops there, Ukraine launched another, highly effective offensive in the northeast, near Kharkiv.

Ukraine has reclaimed the town of Izyum, which has been a Russian logistics hub. Ukraine’s army chief said Sunday that forces have recaptured more than 1,000 square miles of territory in just two weeks’ time — that’s an area equivalent to the size of Rhode Island.

Facing the prospect of a large group of its forces becoming surrounded, Moscow pulled back its troops from Kharkiv in a dramatic shift in the state of play that posed the biggest challenge to the Kremlin since it launched the invasion Feb. 24.

Ukrainian President Volodymyr Zelenskyy praised the military in a video address Saturday night, saying it has reclaimed more than 770 square miles of territory so far this month. He also taunted Moscow over its withdrawal, saying the Russian army was “demonstrating the best it can do — showing its back” and, “They made a good choice to run.”

After capturing the town of Balakliia, about 34 miles southeast of Kharkiv, Ukrainian forces quickly pressed their offensive farther east to Kupiansk, a rail hub vital for sustaining Russian operations in the region.

They claimed control of the strategic city Saturday, cutting supply lines to a big group of Russian forces around Izyum to the south. To prevent their complete encirclement, Moscow ordered the hasty retreat, claiming they were relocating to focus on the neighboring Donetsk region.

Both sides have suffered heavy losses in Europe’s largest conflict since World War II. Ukraine’s military chief said last month that nearly 9,000 of its soldiers have been killed in action. And while Moscow hasn’t reported its own losses since March, Western estimates put the toll as high as 25,000 dead, with the wounded, captured and deserters bringing the overall Russian losses to more than 80,000.

Ukraine has sought to mobilize the population to reach an active military of 1 million people, while Russia, in contrast, has continued to rely on a limited contingent of volunteers for fear that a mass mobilization could fuel discontent and upset internal stability.

The Russian military debacle has provoked outrage among Russian military bloggers and patriotic commentators, who chastised the Kremlin for failing to mobilize more forces and take stronger action against Ukraine. Even Ramzan Kadyrov, the Moscow-backed leader of the Russian region of Chechnya, publicly criticized the Russian Defense Ministry for what he called “mistakes” that made the Ukrainian blitz possible.

As the war slogs on, a growing flow of Western weapons over the summer is playing a key role in the counteroffensive, helping Ukraine significantly boost its precision strike capability.

Since the counteroffensive began, Ukraine said, its forces have reclaimed more than 30 settlements in the Kharkiv region.

The Ukrainian General Staff said Russian forces had also left several settlements in the region but did not identify the towns.

A former commander of pro-Russian forces in the east called the pull-back of troops a “major defeat” on his telegram channel this weekend.

Western experts have called this the worst defeat for Russian forces since they were forced back from Kyiv in the early days of the war.

Russia has ordered its troops to withdraw from Kharkiv oblast in all parts west of the Oskil River, according to the UK Defense Ministry.

The Associated Press contributed to this report.