KYIV, Ukraine — Hundreds of die-hard Ukrainian soldiers who had made a last stand against Russian forces from a Mariupol steel mill faced an uncertain future Tuesday under Kremlin custody after Ukraine’s military ordered them to surrender.
The surrender directive, issued late Monday, made the soldiers prisoners and ended the most protracted battle so far of the nearly three-month-old Russian invasion of Ukraine.
Even as Russia has struggled on other battlefronts, the surrender at Mariupol solidified one of Russia’s few significant territorial achievements — the conquest of a once-thriving southeast port. The surrender also gave Russia’s state-run media the ingredients for claiming its side was winning.
Still, Mariupol has been largely reduced to ruin, Ukrainian officials say that more than 20,000 inhabitants were killed, and the city has come to symbolize the war’s grotesque horrors.
By early Tuesday, many of the fighters ensconced in a warren of shelters under the Azovstal steel mill, a Soviet-era complex besieged by the Russians for weeks, had emerged and surrendered. They were transported to Russian-held territory aboard buses emblazoned with “Z” — the Russian emblem for what President Vladimir V. Putin has called his country’s “special military operation” in Ukraine.
The Ukrainian authorities said little about the terms of the surrender except to assert that the Ukrainian fighters were heroes and that as prisoners they would soon be exchanged for Russian prisoners held by Ukraine.
“The only thing that can be said is that the Ukrainian state is doing everything possible and impossible” to save the soldiers, Ukraine’s deputy defense minister, Hanna Malyar, said at a news conference Tuesday afternoon.
But Russian officials said nothing about an exchange — on the contrary, they raised the prospect that at least some of the prisoners would be treated as war criminals.
Russia’s Investigative Committee, the country’s equivalent to the F.B.I., said Tuesday that investigators would interrogate the captured fighters to “check their involvement in crimes committed against civilians.”
And the prosecutor general’s office asked Russia’s Supreme Court to declare the military unit to which most of the captured fighters belong, the Azov battalion, a terrorist organization. Russian news media have seized on the Azov battalion’s connections to far-right movements to provide a veneer of credibility to the Kremlin’s false claims that Russia’s forces were fighting Nazis in Ukraine.
The Russian threats against the prisoners raised questions about the viability of the terms Ukraine had negotiated with Moscow to surrender, and whether the hundreds of troops still remaining inside the steel plant would abide by the deal.
News of Ukraine’s surrender order to its own fighters, widely seen domestically as heroes who have stared down deprivation and doom, was greeted with anxiety in the country, where antipathy toward Russia has only deepened since the war.
Many expressed fears that the last defenders of Mariupol would suffer as prisoners of Russia — though the most likely alternative was certain death inside the steel works.
“I am waiting for news and praying,” said Natalia Zarytska, who was part of a delegation of wives and mothers of men inside Azovstal who had sought the intervention of Turkey, which has good relations with both Russia and Ukraine, to assure a safe evacuation route for their loved ones.
The Ukrainian government sought to extol the valor of the fighters, who refused to surrender until ordered.
“83 days of Mariupol defense will go down in history as the Thermopylae of the XXI century,” Mykhailo Podolyak, one of President Volodymyr Zelensky’s top advisers, said on Twitter, referring to the 480 B.C. battle in which an outnumbered force of Greeks faced a much larger Persian army. He said the defenders in Azovstal had “ruined” Russia’s plan to capture eastern Ukraine and “completely changed the course of the war.”
Still, the fate of the captured soldiers could create political problems for Mr. Zelensky, whose leadership through the war has boosted his popularity at home and in friendly Western countries.
Mr. Putin could also face an awkward decision over releasing any of the captives — even in a prisoner swap — since he has repeatedly sought to cast Azov battalion members as Nazis. Repatriating them could undercut that fictitious narrative.
Ukraine’s decision to halt the armed defense at the plant appeared to end the last vestige of resistance preventing Russia from fully controlling a swath of southeastern Ukraine stretching from the Russian border to the Crimean Peninsula, which was seized by Russia eight years ago.
The developments in the south underscore how much territory Moscow has captured and suggest that Ukrainian forces will face steep challenges in trying to regain it. At the same time, Ukraine’s military has been emboldened by its successes against Russian forces elsewhere, so the prospects for a negotiated settlement have dimmed.
Both sides acknowledge that talks have basically collapsed amid publicly aired recriminations.
Along a path stretching more than 500 miles from Luhansk in the east to Kherson on the Black Sea, the Ukrainian military said Russian forces were building defensive positions, installing governments with fealty to the Kremlin and taking steps to “Russify” the population.
In Zaporizhzhia, a region west of Mariupol, the Ukrainian military said that Russian forces had been destroying roads and bridges to slow Ukrainian counterattacks. Moscow’s troops also erected concrete barriers and dug trenches around Europe’s largest nuclear power plant, in the city of Enerhodar, which Russia seized in the first month of the war, Ukraine’s nuclear power company said.
In the Russia-occupied Kherson region, the nation’s agricultural heartland, the Ukrainians have been mounting counterattacks for weeks, slowly trying to reclaim lost ground, but have yet to launch a major offensive.
The Ukrainian military said Tuesday evening that Russia was taking steps to prepare for a long-term military occupation. “The war is entering a protracted phase,” the Ministry of Defense said in a statement. “We see how in the Kherson region, in the Zaporizhzhia region, the Russian invaders are actively carrying out engineering and fortification work to move to defense if necessary.”
Still, Ukrainian forces, backed by an increasing flow of heavy weapons from Western allies, have mounted fierce resistance on other battle fronts, driving Russian forces first from the capital, Kyiv, and in recent days from the northeastern city of Kharkiv.
Ukrainian officials said Tuesday that more than 50 “seriously injured” fighters from Mariupol were being transported to a hospital in Novoazovsk, a Ukrainian town near the Russian border that is controlled by Moscow-backed separatists. Another 211 people were evacuated via a humanitarian corridor to Olenivka, also under Russian control.
Ukrainian officials said that the soldiers would be returned to Ukrainian-held territory “under an exchange procedure.”
However, it was unclear who was guaranteeing the security of the servicemen and whether any procedure had been agreed upon before the evacuation began.
“Those 211 people who were evacuated to Olenivka, their fate is paramount to negotiate about right now,” Kira Rudik, a member of parliament and leader of the Holos party, involved in negotiations about Azovstal, said on Tuesday afternoon.
In recent days, Western countries have reaffirmed their support for Ukraine, and against Russian interests.
The leaders of Sweden and Finland said Tuesday that they would jointly submit their applications to join the NATO alliance this week and would visit Washington to meet with President Biden, who strongly supports their plans.
In Brussels, Treasury Secretary Janet L. Yellen exhorted European Union nations to increase their spending on Ukraine to help it cope with the economic crisis and rebuilding that will be required because of the Russian invasion.
“Our joint efforts are critical to help ensure Ukraine’s democracy prevails over Putin’s aggression,” Ms. Yellen, in the midst of a weeklong trip to Europe, told the Brussels Economic Forum.
Congress has already approved a $13.6 billion emergency spending package for Ukraine and is expected to approve a further $40 billion worth of aid.
Valerie Hopkins reported from Kyiv, Marc Santora from Krakow, Poland, Ivan Nechepurenko from Tbilisi, Georgia, and Rick Gladstone from New York. Reporting was contributed by Alan Rappeport from Brussels, Safak Timur from Istanbul, and Johanna Lemola from Helsinki.