Russia releases 215 fighters, including Mariupol commanders, in a prisoner exchange.

Ukrainian authorities have secured the release of the commanders of the Azov Battalion, whose defense of Mariupol from within a sprawling steel plant turned them into celebrities throughout Ukraine and made them a valuable prize for the Kremlin when they surrendered to Russian forces in May after an 80-day siege.

Andriy Yermak, a top adviser to President Volodymyr Zelensky of Ukraine, confirmed late Wednesday that the commander of the Azov Battalion, Denis Prokopenko, and his deputy, Captain Svyatoslav Palamar, were among 215 Ukrainian prisoners of war who were released in a prisoner swap, making it the largest such exchange since the start of the war.

“President Volodymyr Zelensky gave a clear order to return our heroes. The result: our heroes are free,” Mr. Yermak said.

A senior Ukrainian military official, who spoke on the condition of anonymity because details of the exchange had not yet been publicly announced, did not indicate when exactly the exchange occurred, though Ukrainian media outlets began publishing photos late Wednesday evening Kyiv time of what they said were the newly freed commanders.

The official said the soldiers had been traded for 55 people, including senior Russian officers and Viktor Medvechuk, a Ukrainian oligarch and close friend of the Russian president, who was arrested at the start of the war and charged with treason.

Also among the newly freed prisoners were two Americans who were members of Ukraine’s foreign legion, a group of foreign fighters who have taken part in some of the bloodiest battles in the war.

The exchange represents a significant victory for Mr. Zelensky, who had vowed to bring home all prisoners of war. Returning the Azov commanders in particular is likely to provide another morale boost to Ukrainian forces across the front line, and comes after Russian forces were routed in the northeast.

Video of President Zelensky appeared on YouTube late Wednesday, showing him speaking to the Azov commanders, who have been released to Turkey.

Among those released were 108 members of the Azov Battalion, a unit within the Ukrainian armed forces that Russian propaganda has attempted to paint as neo-Nazis as part of the Kremlin’s justification for war.

The Azov soldiers’ defense of Mariupol, the southern Ukrainian port city decimated by Russian forces in the first months of the war, has become a source of inspiration and pride for Ukrainians, with the commanders’ likenesses displayed on billboards around the country.

For 80 days, the band of soldiers, wildly outnumbered and outgunned by Russian forces, continued to fight despite heavy losses and a severe lack of food, water and weaponry.

Their surrender in May raised fears that the Kremlin could use them as propaganda, perhaps by staging show trials. That Russia would release such valuable prisoners suggests that Ukrainian forces had in their possession valuable prisoners of their own. The 55 people handed over to Russian forces included pilots and senior officers, the Ukrainian official said.