Ukrainian Troops Advance in East as Kyiv Seizes the Initiative

The dual offensives in eastern and southern Ukraine show how the country’s military is increasingly forcing Russia to react to its moves. Ukraine’s forces are growing gradually stronger as the country receives advanced weapons from the U.S. and other Western countries, while Russia is struggling to deploy extra well-trained manpower after suffering heavy losses since it launched its full-scale invasion in February.

Russia still holds an advantage in the quantity of artillery and shells, however, and advancing remains difficult for either side’s forces, particularly across the flat and open ground that characterizes large parts of eastern and southern Ukraine.

After pushing Russian troops back from the Ukrainian capital of Kyiv this spring, Ukrainian forces had been gradually retreating from cities in the east that Russia was leveling with artillery and airstrikes. But Russia’s eastern offensive appears exhausted, with manpower and supply shortages exacerbated by Ukraine’s use of long-range rockets provided by the U.S. to strike command posts and ammunition and fuel depots.

One target of the offensive is the city of Kupyansk, a road hub for Russian supplies heading south from the border into eastern Ukraine. A continued Ukrainian advance could also threaten to isolate Russian forces in the city of Izyum, which Russia has been seeking to use as a staging point for its own offensive in eastern Ukraine.

Ukrainian forces surrounded the city of Balakliya on Tuesday and advanced along a road northeast, seizing villages, according to Russian bloggers who are close to the Russian military. Ukraine’s military didn’t comment, but an adviser to President

Volodymyr Zelensky

confirmed the gains.

“There are surprises along the whole front,” said the adviser,

Oleksiy Arestovych.

Russia’s Defense Ministry on Wednesday didn’t comment on Ukraine’s eastern counteroffensive but said Russian forces had successfully struck Ukrainian targets in Kharkiv and the eastern Donetsk region. The ministry added that Ukraine had paused its counteroffensive in the south over the past day after incurring large losses in manpower and military equipment.

Also on Wednesday, Russian President

Vladimir Putin

signaled defiance in the face of Ukraine’s counteroffensives, saying Moscow had only gained from the invasion and that it would continue the military campaign “until the end,” in comments at an economic forum.

The advance near Kharkiv comes a week after Ukraine launched an offensive in the south, retaking several villages and expanding a bridgehead across the Inhulets River. Ukraine is trying to cut off thousands of Russian troops in the southern regional capital of Kherson, which Russia seized early in its invasion.

Ukraine also claimed fresh success in the south on Wednesday, seizing a village and striking Russian military facilities, pontoon bridges used to supply troops in Kherson and ammunition depots.

Ukraine spoke openly of its intention to launch a southern offensive, prompting Russia to reinforce its units in the south with thousands of troops from the east. That appears to have opened opportunities for Ukrainian forces in the east to advance.

“Russia’s deployment of forces from Kharkiv and eastern Ukraine to Ukraine’s south is likely enabling Ukrainian counterattacks of opportunity,” the Institute for the Study of War, a Washington-based think tank, wrote in an analysis late Tuesday.

Mr. Arestovych, the Ukrainian presidential adviser, said multiple offensives were keeping the Russians off balance and leaving them unable to shore up all positions with reserves.

“It’s clear who has the initiative at the moment,” he said.

On Tuesday, Ukraine said its forces had also made limited advances in the eastern region of Luhansk, almost all of which was captured by Russia during its now-stalled eastern offensive.

—Olya Fokaf contributed to this article.

Write to James Marson at james.marson@wsj.com