Ukrainian forces trying to punch through Russian lines are facing perhaps their biggest test of the war as, according to two Pentagon officials, Kyiv begins the main thrust of its counteroffensive, pouring the bulk of their Western-trained reserves into the fight to sever Moscow’s hold on the south.
The task facing the advancing Ukrainian troops is monumental. Since seizing Ukrainian territory in last year’s invasion, Russia has built a dense defensive web of minefields, trenches, bunkers, tank traps and other obstacles. That has made the counteroffensive slow going, frustrating Ukrainians and international supporters.
The Ukrainians mounted a “massive” assault with three battalions, reinforced with tanks, south of the town of Orikhiv, and then another a few miles farther south near the village of Robotyne, said Igor Konashenkov, a spokesman for Russia’s defense ministry, according to Tass, a state news agency. Both were repelled, the ministry said. The area around Orikhiv is one of three main axes of assault.
Other American officials said that the most recent Ukrainian attack might be preparatory operations for the main thrust or reinforcements to replenish war-weary units.
One of Ukraine’s military objectives is to drive south from the current front line through the town of Tokmak to the city Melitopol near the coast. Both are highway and railroad hubs, and driving a wedge that deep would effectively split the Russian-held territory in two, making resupply and coordination more difficult for Moscow’s forces.
The United States and other allies have trained about 63,000 Ukrainian troops, according to the Pentagon, and have supplied more than 150 modern battle tanks, a much larger number of older tanks, hundreds of infantry fighting vehicles and thousands of other armored vehicles.
American officials, who spoke on the condition of anonymity to discuss internal deliberations, said on Wednesday that most of those reserves had been committed. All along the southern front on Wednesday, heavy artillery fire was heard as Ukrainian guns fired from hidden positions and the Russian guns responded, hitting positions their troops had recently abandoned.
Local occupation officials reported fierce battles raging south of Orikhiv, involving brigades of foreign-trained troops and armor donated by the United States and Germany.
At the same time, Russia mounted a missile barrage on Wednesday at targets across Ukraine, launching about three dozen cruise missiles and four hypersonic ballistic missiles from aircraft.
“There were a few hits, and some missile fragments fell,” President Volodymyr Zelensky of Ukraine said in his nightly address on Wednesday, without providing details.
Mr. Zelensky was vague about the counteroffensive. “Today our guys at the front had very good results,” he said. “More details later.”