Ukrainian President Volodymyr Zelenskiy visited troops on the front line in the eastern Donetsk region as fighting appeared to cease around Russia's Belgorod region a day after armed fighters from inside Ukraine launched one of the largest cross-border incursions since the start of the war.
The Russian Defense Ministry on May 23 claimed that its troops had surrounded enemy fighters and used "air strikes, artillery fire, and active action by border units" to push back the forces, killing many of them.
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It was not possible to independently confirm the claims, but the governor of the Belgorod region, Vyacheslav Gladkov, said so-called anti-terrorism measures introduced earlier had been called off.
And one of two groups claiming to be behind the raid -- the Russian Volunteer Corps (RVC) -- said on social media that "one day we will return to stay."
The RVC and the Freedom of Russia Legion claimed responsibility for the incursion that shocked local residents and Russian authorities. They said they were anti-Kremlin Russian fighters seeking to overthrow President Vladimir Putin.
It was not immediately clear if the fighters had crossed back into Ukraine after battling in several border-area villages.
The incursion into Russian territory may be the biggest since the Kremlin launched its war against Ukraine 15 months ago and underscores Moscow’s overall lack of manpower.
The Ukrainian government has denied any role in the events.
Upon return from an extended trip abroad, Zelenskiy traveled to the front on May 23 and congratulated the military on Ukrainian Marine Corps Day. He posted pictures of himself handing out medals to fighters at a site near the southern Ukrainian city of Vuhledar.
"Every day on the battlefield, Ukrainian marines prove they are a powerful force that destroys the enemy, liberates Ukrainian land, and performs the most difficult tasks in most difficult conditions," Zelenskiy said.
WATCH: A reserve colonel in the Ukrainian armed forces says that fighting in Russia's Belgorod region was a "combat reconnaissance mission" launched by units of Russian citizens that have been fighting on Kyiv's side since 2014.
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'Combat Reconnaissance': What's Behind A Second Incursion Into Russia?
"From today," he added, "we are significantly increasing the potential of the marines and creating a Marine Corps."
Both sides claim successes in the eastern city of Bakhmut, with Russia saying it now had the city under its control after a monthslong battle that is estimated to have caused thousands of casualties.
The Ukrainian military says fighting continues in and around Bakhmut, with Ukrainian forces repelling 30 Russian assaults over the past day in the city.
Ukrainian forces made some progress on the northern and southern flanks of Bakhmut, General Oleksandr Syrskiy, commander of Ukraine’s ground forces, said on May 23.
"The battle continues. Our defense forces are making progress on the flanks," Syrskiy wrote on Telegram.
Deputy Defense Minister Hanna Malyar wrote separately on Telegram that fighting in the city has decreased overall, though it continues in the suburbs.
Malyar said Ukrainian progress in Bakhmut is "insignificant," but Russia is sustaining "great losses."
Ukraine’s military general staff said on May 23 there had been no missile attacks in Ukraine over the past 24 hours, but it said Russian forces launched some two dozen air strikes and artillery fire to blast several towns and villages.
Ukrainian Forces Still Fighting For Bakhmut Despite Moscow's Claim Of Victory
"There are, unfortunately, dead and wounded civilians and private homes, and administrative infrastructure have been damaged," it said.
On the diplomatic front, NATO Secretary-General Jens Stoltenberg rejected claims by the Kremlin that the training of Ukrainian pilots on U.S.-produced F-16 fighter jets made NATO a participant in the war.
"We help Ukraine to uphold that right [to defend itself]. That doesn't make NATO and NATO allies a party to the conflict," he told reporters in Brussels.
Valeriy Zaluzhniy, commander-in-chief of Ukrainian forces, said he had a telephone conversation with the U.S. supreme allied commander in Europe, General Christopher Cavoli.
Zaluzhniy said in a Facebook post that the two discussed the need to strengthen Ukraine's air defense, in particular with the help of F-16 fighters, and increase the supply of ammunition.