The International Committee of the Red Cross said Thursday that it has registered hundreds of Ukrainian prisoners of war from a besieged steel plant in war-ravaged Mariupol this week, after the Ukrainian city fell into Russian hands.

A team from the ICRC began on Tuesday to register combatants leaving the Azovstal Iron and Steel Works plant, including the wounded, at the request of the parties to the conflict. The operation continued Wednesday and was still ongoing Thursday. The ICRC is not transporting prisoners of war to the places where they are held, according to a press release from the organization.

"The registration process that the ICRC facilitated involves the individual filling out a form with personal details like name, date of birth and closest relative," the organization said. "This information allows the ICRC to track those who have been captured and help them keep in touch with their families."

The Geneva-based humanitarian agency, which has been working in Ukraine since 2014, noted that it "maintains a confidential dialogue with the parties to the conflict on their obligations under international humanitarian law."

"In accordance with the mandate given to the ICRC by States under the 1949 Geneva Conventions, the ICRC must have immediate access to all POWs in all places where they are held," the organization added. "The ICRC must be allowed to interview prisoners of war without witnesses, and the duration and frequency of these visits should not be unduly restricted. Whenever circumstances permit, each party to the conflict must take all possible measures to search for and collect the dead."

For weeks, Ukrainian fighters and civilians were holed up inside Mariupol's vast Azovstal plant as the remaining pocket of Ukrainian resistance to Russia's relentless bombardment of the strategic southeastern port city. Russia claimed Thursday that 1,730 Ukrainian fighters had surrendered in Mariupol over the previous three days, while Ukraine confirmed Tuesday that more than 250 had yielded in the initial hours after it ordered them to do so.

Mariupol is the largest city that Russian forces have seized since launching an invasion of neighboring Ukraine on Feb. 24. Its complete capture gives Russia total control of the coast of the Sea of Azov as well as a continuous stretch of territory along eastern and southern Ukraine.

-ABC News' Max Uzol

Russia has fired senior military commanders in recent weeks "who are considered to have performed poorly during the opening stages of its invasion of Ukraine," the U.K. Ministry of Defense said Thursday in an intelligence update.

According to the ministry, Lt. Gen. Serhiy Kisel, who commanded Russia's elite 1st Guards Tank Army, has been suspended for his failure to capture Ukraine's second-largest city, Kharkiv. Vice Adm. Igor Osipov, who commanded Russia's Black Sea Fleet, has also likely been suspended following the sinking of the fleet's flagship, Moskva, in April. Gen. Valeriy Gerasimov, the Russian military's chief of the general staff, likely remains in his post, but it was unclear whether he retains the confidence of Russian President Vladimir Putin, according to the ministry.

"A culture of cover-ups and scape-goating is probably prevalent within the Russian military and security system," the ministry said. "Many officials involved in the invasion of Ukraine will likely be increasingly distracted by efforts to avoid personal culpability for Russia’s operational set-backs."

"This will likely place further strain on Russia's centralised model of command and control, as officers increasingly seek to defer key decisions to their superiors," the ministry added. "It will be difficult for Russia to regain the initiative under these conditions."

Russia has placed two Ukrainian commanders on a wanted list.

Serhiy Velychko and Kostiantyn Nemychev, commanders of the Azov Regiment, a far-right group now part of the Ukrainian military, have been added to the Russian Ministry of Internal Affairs' database of wanted fugitives in connection with a criminal case.

According to the Russian Investigative Committee, Velychko and Nemychev are accused of attempted murder of at least eight Russian servicemen who sustained multiple injuries in eastern Ukraine's Kharkiv region. Criminal charges were brought against the pair in absentia, and Russian authorities are working to track down and apprehend them.

The Senate on Wednesday night unanimously confirmed the new U.S. ambassador to Ukraine, Bridget Brink, a career foreign service officer.

The vote took place on the same day the U.S. officially resumed operations at its embassy in Kyiv.

-ABC News' Trish Turner

White House national security advisor Jake Sullivan hinted Thursday of more sanctions coming against Russia in the "next week or two" aimed at targeting ways Moscow is evading sanctions already imposed.

“Where our focus will be over the course of the coming days is on evasion,” Sullivan said Thursday at the Economic Club of Washington. “As Russia tries to adjust to the fact that it’s under this massive economic pressure, what steps do they take to try to evade our sanctions and how do we crack down on that? And I think we'll have some announcements in the next week or two that identify targets that are trying to facilitate that evasion both inside Russia and beyond."

When Sullivan was asked whether sanctions will automatically be lifted if a negotiated peace deal between Russia and Ukraine is worked out, he appeared cautious with his words, saying, “a lot of that depends on what the shape and scope” of the agreement is.

“A lot of it depends on what the Ukrainians, in consultation with us and the Europeans come to agree to," Sullivan said. "You know, we're not going to do a deal over the head of the Ukrainians where we give a bunch of sanctions relief to Russia. But if some measure of sanctions relief were built in to some credible diplomatic solution led by the Ukrainians, that's something that we would happily discuss."

But Sullivan said Russian oligarchs shouldn't expect to ever get back their yachts and other assets seized under sanctions that have been imposed, saying the ultimate goal is "not to give them back” once the war is over.

“The president is actively looking at how we can deal with the fact that as we seize these assets, our goal is not to give them back. Our goal is to put them to a better use than that," Sullivan said. "But I'll be careful in what I say today because there's an ongoing kind of policy process around how we end up dealing with that question. But, rest assured, that the goal is not just to sit on them for a while."

-ABC News' Justin Gomez