After piercing a daunting line of Russian defenses around the southern village of Robotyne, Ukrainian forces are now seeking to take the next step in their arduous counteroffensive, waging a fierce battle a few miles farther to the east, according to Ukrainian military commanders and U.S. officials.
The intense fighting on Thursday comes amid weeks of brutal battles that have resulted in small but significant advances that Ukrainian forces are trying to exploit, with the broader goal of driving a wedge into the so-called land bridge between Russia and occupied Crimea, which is vital to the Russian military’s supply routes.
The Ukrainian 46th Brigade, which is participating in the fighting in the area, said that its assault units were attacking Russian positions near the village of Verbove, nine miles east of Robotyne.
The move toward Verbove is notable because it shows that Ukraine is confident enough in its hold on Robotyne that it believes its troops can try to press forward.
U.S. officials on Thursday confirmed that Ukrainian forces had punched through a major line of Russian defenses around Robotyne and were engaged in fighting near Verbove.
Even such small advances are significant, American officials said, because they have generated the first real Ukrainian momentum in weeks and pushed their artillery and missiles a bit closer to strike deeper into Russian-held territory at Moscow’s troops, supplies and transportation networks.
A senior Western military official said the Ukrainian advances, while noteworthy, do not yet represent a major operational breakthrough. But they provide a morale boost for both Ukrainian troops and public sentiment, and demonstrate real progress to the United States and other allies that have provided Ukraine with billions of dollars in arms and equipment, the official said.
Western analysts noted that several other defensive lines converge around Verbove, which could slow or stall the advance.
Ukrainian military officials themselves have warned not to expect rapid progress, with every bit of ground retaken exacting a toll on their troops. And as Ukrainian forces look to push south toward the Sea of Azov, there are still miles of formidable Russian defenses ahead — including mines, tank traps, fortified trenches, concrete pill boxes and sniper nests.
On Thursday, the 46th Brigade said its soldiers had reached the western part of Verbove, though it underlined that there were much more difficult fights ahead.
“The battles will be for heights farther south and southwest,” the brigade said. The brigade cautioned against “hype” since even if it can punch through the next defensive line, Russia has still more ahead.
As they aim to push forward, Ukrainian forces also have to defend against Russian efforts to propel them back again.
“Russia is constantly counterattacking, conducting an active defense,” the brigade said, adding that “our month of battles has shown that the enemy is not going to give up the captured lands — there is a lot of work ahead.”
The Institute for the Study of War, a Washington-based think tank, said in its latest analysis that geolocated combat footage published on Wednesday showed that Ukrainian forces had advanced to the northwestern outskirts of Verbove, though the extent of those advances and control over these positions remained unclear.
If Ukraine can hold the ground it recently reclaimed, its forces would be in a position to apply pressure on Russian supply routes running through the city of Tokmak, about 15 miles to the south.
Just as important as the Ukrainian advance, military analysts said, is the Russian reaction to the headway. It is not clear how many reserve soldiers Russia can bring to this sector of the front without creating weaknesses the Ukrainians can exploit elsewhere.
“The Ukrainians are gradually gaining ground, which means that they are pushing the Russians back, and they can break through some of these well-fortified areas,” Jens Stoltenberg, NATO’s secretary general, told CNN on Wednesday, noting that “Ukrainians have exceeded expectations again and again.”
Dmytro Kuleba, Ukraine’s foreign minister, offered an example of the difficulty of the battle during a meeting of diplomats in France on Wednesday. After the units spent more than two months engaged in a grueling campaign to break the Russian lines around Robotyne, their fighting capability was exhausted, he said.
The local commander asked for permission to restructure the attack force there, choosing 31 soldiers considered to be deeply motivated. A third of these had no combat experience, he said.
To recapture Robotyne, these selected soldiers first had to take a tree line outside the village.
“It’s in these plantations, invisible on maps, that the greatest tragedies and heroism of the war take place,” Mr. Kuleba said. “So our unit drove the Russians out of there and held the position for two days until reinforcements arrived.”
The soldiers then had to walk some six miles through fields laden with mines to reach the village itself.
“They only had time to catch their breath briefly and immediately stormed the fortified Russian positions, drove the enemy out and held out until the main forces arrived,” Mr. Kuleba said.
Over the course of 40 days, he said, this unit conducted six assaults and two reconnaissance missions. Seven of the soldiers were wounded, he said, including one who stepped on a mine.
“The work of this group made it possible for an entire brigade to attack Robotyne and liberate it after weeks of assaults,” he said. “After securing its flanks, we open the way to Tokmak and, ultimately, Melitopol and the border with Crimea.”
According to American officials, Russian attack helicopters that stymied advancing Ukrainian tanks and armored personnel carriers earlier in the three-month-old offensive have been more effectively countered recently by Ukrainian troops firing Stinger antiaircraft missiles. And cluster munitions provided by the Pentagon have also effectively attacked Russian troops caught out in the open, these officials said.
Still, military analysts said on Thursday that Ukraine has had to tap into forces for this assault phase near Robotyne that commanders had initially planned to keep in reserve, including units equipped with dozens of U.S. Army Stryker combat vehicles.
A big concern for Ukrainian commanders now is whether they will have enough combat power left to exploit breaches in the formidable Russian minefields and other defenses, and then widen those holes in the lines as they continue to push south toward their ultimate goal.
Marc Santora reported from Odesa, Ukraine, Constant Méheut from London, and Eric Schmitt from Washington.