More and more Ukrainian fighters who were making a last stand in Mariupol have surrendered, bringing the total who have left their stronghold to 1,730, the Russian military said Thursday, while the International Committee of the Red Cross (ICRC) registered hundreds of them as prisoners of war.

The ICRC said that the registrations of Ukrainian prisoners of war, which included wounded fighters, began Tuesday under an agreement between Russia and Ukraine.

The Geneva-based humanitarian agency, which has experience in dealing with prisoners of war and prisoner exchanges, said however that its team did not transport the fighters to "the places where they are held" – which was not specified.

Ukrainian fighters who emerged from the ruined Azovstal steelworks after being ordered by their military to abandon the last stronghold of resistance in the now-flattened port city face an uncertain fate. Some were taken by the Russians to a former penal colony in territory controlled by Moscow-backed separatists.

While Ukraine said it hopes to get the soldiers back in a prisoner swap, Russia threatened to put some of them on trial for war crimes. The Russian parliament was scheduled to consider a resolution to ban the exchange of any Azov Regiment fighters but did not take up the issue Wednesday.

The Red Cross cited rules under the Geneva Conventions that should allow the organization to interview prisoners of war "without witnesses" and that visits with them should not be "unduly restricted." The organization did not specify how many prisoners of war were involved. It is also not clear how many fighters are left at the plant. Russia previously estimated that it had been battling some 2,000 troops in the waterside plant.

Moscow claims a surrender on a far bigger scale than Kyiv has acknowledged since ordering its garrison to stand down.

The ultimate outcome of Europe's bloodiest battle for decades remained publicly unresolved, with no confirmation of the fate of the hundreds of Ukrainian troops who had held out in a vast steelworks at the end of a near three-month siege.

Ukraine, which says it aims to secure a prisoner swap, has declined to say how many were inside the plant or comment on the fate of the rest since confirming that just over 250 had surrendered in the initial hours after it ordered them to yield.

The leader of Russian-backed separatists in control of the area said nearly half of the fighters remained inside the steelworks, where underground bunkers and tunnels had protected them from weeks of Russian bombardment.

"More than a half have already left – more than half have laid down their arms," Denis Pushilin told the Solovyov Live internet television channel. "Let them surrender, let them live, let them honestly face the charges for all their crimes."

The wounded had been given medical treatment while those who were fit had been taken to a penal colony and were being treated well, he said.

Amnesty International said earlier that the Red Cross should be given immediate access to the Mariupol fighters who surrendered. Denis Krivosheev, Amnesty’s deputy director for the region, cited lawless executions allegedly carried out by Russian forces in Ukraine and said the Azovstal defenders "must not meet the same fate."

Mariupol was a target of the Russians from the outset as Moscow sought to open a land corridor from its territory to the Crimean Peninsula, which it seized from Ukraine in 2014. The city – its prewar population of about 430,000 now reduced by about three-quarters – has largely been reduced to rubble by relentless bombardment, and Ukraine says over 20,000 civilians have been killed there.

For Ukraine, the order to the fighters to surrender could leave President Volodymyr Zelenskyy's government open to allegations it abandoned the troops he described as heroes.

"Zelenskyy may face unpleasant questions," said Volodymyr Fesenko, who heads the independent Penta think tank in Kyiv. "There have been voices of discontent and accusations of betraying Ukrainian soldiers."

Donbass attack

On the battlefront, Russian forces pressed their main offensive, trying to capture more territory in the eastern Donbass region which Moscow claims on behalf of separatists.

Ukraine's general staff said in a statement on Thursday that Russia's attacks were focused on the Donetsk region. Russian forces "suffered significant losses" around Slovyansk to the north of Donetsk.

Police said on Telegram on Thursday that two children had been killed in the Donetsk city of Lyman in a direct hit on a residential building.

Ukrainian forces shelled a border village in Russia's western region of Kursk at dawn on Thursday, killing at least one civilian, regional governor Roman Starovoit said.

Ukraine's military made no mention of Mariupol in its early morning briefing Thursday, saying only that Russian forces were still pressing their offensive on various sections of the front in the east, but were being successfully repelled.

On the Russian side of the border, the governor of Kursk province said a truck driver was killed and several other civilians wounded by shelling from Ukraine. Separatist authorities in the Donetsk region in eastern Ukraine said two civilians were killed and five wounded also in Ukrainian shelling over the last 24 hours.

Meanwhile, in the first war-crimes trial held by Ukraine, a captured Russian soldier pleaded guilty on Wednesday to killing a civilian and faces possible life in prison. In the war-crimes case in Kyiv, Russian Sgt. Vadim Shishimarin, a 21-year-old member of a tank unit, pleaded guilty to shooting an unarmed 62-year-old Ukrainian man in the head through a car window in the opening days of the war. Ukraine's top prosecutor has said some 40 more war-crimes cases are being readied.

Military analysts, though, said the city's capture at this point would hold more symbolic importance than anything else, since Mariupol is already effectively under Moscow's control and most of the Russian forces that were tied down by the drawn-out fighting have already left.

On the diplomatic front, Finland and Sweden could become members of NATO in a matter of months, though objections from Turkish President Recep Tayyip Erdoğan threaten to disrupt things. Turkey accuses the two countries of harboring terrorist groups that it considers a threat to its security.

Ibrahim Kalın, a foreign policy adviser and spokesperson for Erdoğan, said there will be "no progress" on the membership applications unless Turkey's concerns are met. Each of NATO’s 30 countries has an effective veto over new members.