(CNN) Ukrainian forces have completed their "combat mission" in Mariupol, according to a statement by the country's military, bringing the months-long battle for the besieged city close to an end.
Commanders of units stationed at the city's massive Azovstal steelworks plant have been ordered "to save the lives of their personnel," the statement by the General Staff of the Armed Forces of Ukraine added.
Hundreds of people were evacuated on Monday from the steel plant, the last holdout in a city that had become a symbol of Ukrainian resistance under relentless Russian bombardment.
Ukraine's Deputy Defense Minister Hanna Malyar described the evacuation operation in a separate video statement, noting that some Ukrainian forces remain at Azovstal.
"Fifty-three seriously injured people were evacuated from Azovstal to a medical facility in Novoazovsk for medical care," she said. "Another 211 people were taken to Olenivka through the humanitarian corridor."
An "exchange procedure" will see the evacuees eventually brought home, Malyar also said.
According to Malyar, the defense of Mariupol meant Russian forces were not able to transfer about 20,000 personnel to other regions of Ukraine, and thus failed to capture Zaporizhzhia.
Also on Tuesday, Malyar told journalists that the evacuation was the only way Azovstal's defenders could be rescued.
"Unfortunately, military unblocking is impossible in this situation. There could be no other way to rescue them than the way it is happening now. It was the only way out," Malyar said during a briefing at the Media Center Ukraine.
Iryna Vereshchuk, Ukraine's deputy prime minister, also said that Ukraine expects to carry out an exchange of Russian prisoners of war for the severely injured soldiers evacuated from Azovstal.
Kremlin spokesman Dmitry Peskov said Tuesday that the fighters who left the plant will be treated in accordance with international law, adding on a regular conference call that Russian President Vladimir Putin allowed both civilians and the military to leave Azovstal after the troops laid down their arms.
The Russian Investigative Committee said it would interrogate what it described as "the surrendered militants" in a statement published Tuesday.
Ukrainian President Volodymyr Zelensky addressed the evacuation in a statement Monday, thanking the Ukrainian military and negotiators, the International Committee of the Red Cross and the United Nations.
"Ukraine needs Ukrainian heroes alive," he said.
"The 82nd day of our defense is coming to an end. A difficult day. But this day, like all others, is aimed precisely at saving our country and our people," Zelensky said.
The Russian Defense Ministry had earlier said that a ceasefire had been established to allow the passage of wounded Ukrainian servicemen, according to state news agency RIA Novosti.
Mariupol, a port city on the Sea of Azov, has been the scene of some of the most intense fighting in Ukraine since Russia launched its invasion in late February.
Many civilians have already been evacuated. But Ukrainian fighters in the city had, in April, vowed to "fight until the end," despite being surrounded, low on ammunition and outnumbered by Russian forces.
Russian TV network RT on Monday showed video of around 10 to 12 buses leaving the steel plant. The buses appeared to be a mixture of hospital and ordinary transport, some marked with a red cross.
In her statement, Malyar credited "the defenders of Mariupol" for gaining Ukraine "critical time to form reserves, regroup forces and receive assistance from partners."
"Unfortunately, we do not have the opportunity to unblock Azovstal by military means," she said.
The country's Azov Regiment on Monday also issued a statement saying "the entire Mariupol garrison" was following orders to save lives.
"In order to save lives, the entire Mariupol garrison is implementing the approved decision of the Supreme Military Command and hopes for the support of the Ukrainian people," the Azov Regiment said in a statement late Monday.
"The defenders of Mariupol fulfilled the order, despite all the difficulties, and distracted the overwhelming forces of the enemy for 82 days."