Russia's Defense Ministry says 771 Ukrainian fighters at the Azovstal steel plant in Mariupol -- Ukraine's last stronghold in the besieged southern port city -- have "surrendered" in the last 24 hours, taking the total to 1,730 since May 16 as the Red Cross began registering "hundreds" of them.

The ministry said 80 of those who gave themselves up were wounded. All of them were reportedly transferred to territory in eastern Ukraine that is controlled by Kremlin-backed separatists.

There was no independent confirmation of the figure, and no indication of the fate of the troops still holed up in the compound. Moscow and Kyiv have given different estimates on the number of Ukrainian soldiers who were extracted from Azovstal.

Ukrainian Deputy Defense Minister Hanna Malyar said on May 18 that negotiations for their release were ongoing.

The International Committee of the Red Cross (ICRC) said it had started registering hundreds of prisoners of war (POWs) who were taken by Russia from Azovstal.

"Over the last 2 days, we’ve registered hundreds of prisoners of war leaving the Azovstal plant in Mariupol. Registering POWs is an essential part of our work. It's critical to ensure they're accounted for & treated humanely and with dignity," the ICRC said on Twitter on May 19.

The ICRC said in a statement that the registration process, which is ongoing, involves documenting personal details such as name, date of birth, and closest relatives.

This "allows the ICRC to track those who have been captured and help them keep in touch with their families," the statement said.

It added that under the Geneva Conventions, the ICRC is allowed to interview prisoners of war "without witnesses" and that visits with them should not be "unduly restricted."

Meanwhile, the Ukrainian military said Russian forces launched counterattacks around Kharkiv in an attempt to regain lost ground after being pushed back to the border.

In the area of the Velyka Komyshuvakha settlement, Russian forces suffered significant losses and were forced to withdraw to previously occupied positions, Ukraine's General Staff said on May 19.

The governor of the Russian region of Kursk said on May 19 that one person was killed and several wounded after what he said was a Ukrainian attack on a village near the border.

The British Ministry of Defense said in its daily intelligence bulletin on May 19 that Lieutenant General Sergei Kisel, who commanded the elite 1st Guards Tank Army, has been suspended for his failure to capture Kharkiv.

The British intelligence report said that Kisel was just one of the senior Russian officers who have been fired in recent weeks for their poor performance during the early stages of the invasion of Ukraine.

Among other Russian commanders who have likely been dismissed is Vice Admiral Igor Osipov, who commanded Russia’s Black Sea Fleet, following the sinking of the cruiser Moskva in April, British intelligence reported.

Valery Gerasimov, the chief of the General Staff of the Russian military, likely remains in his post, the bulletin said, adding that it was unclear whether he retains President Vladimir Putin's confidence.

A culture of cover-ups and scapegoating is probably prevalent within the Russian military and security system, the British bulletin said, concluding that this could place further strain on Russia's centralized model of command and control and make it more difficult for Moscow to regain the initiative in the conflict.

Meanwhile, an unnamed NATO military official with knowledge of the intelligence told CNN that the momentum in the conflict had shifted significantly in favor of Ukraine, although the alliance doesn't expect significant gains for either side in the coming weeks.

On the diplomatic front, U.S. President Joe Biden will host the leaders of Finland and Sweden on May 19 to discuss their NATO membership bids.

On May 18, the United States said it was reopening its embassy in Kyiv, and the U.S. Senate Foreign Relations Committee unanimously approved President Joe Biden's nominee to be the next U.S. ambassador to Ukraine.

"The Ukrainian people...have defended their homeland in the face of Russia's unconscionable invasion, and, as a result, the Stars and Stripes are flying over the Embassy once again," U.S. Secretary of State Antony Blinken said in a statement announcing the reopening of the embassy.

The nomination of veteran diplomat Bridget Brink is expected to easily win a vote in the full Senate after clearing the committee.