Dozens of civilians trapped for weeks inside a steel plant in the devastated Ukrainian city of Mariupol were expected to reach Zaporizhzhia on Monday, according to Ukrainian President Volodymyr Zelenskyy.

In a statement posted to Twitter on Sunday, Zelenskyy said a first group of about 100 people were already en route to the Ukrainian government-controlled city, about 140 miles northwest of Mariupol.

"Tomorrow we'll meet them in Zaporizhzhia," Zelenskyy tweeted. "Grateful to our team!"

Many more civilians remain trapped at the sprawling Azovstal Iron and Steel Works plant in Mariupol -- the last holdout of Ukrainian resistance to Russia's bombardment of the strategic southeastern port city -- which Russian forces resumed shelling overnight.

"Today, for the first time in all the days of the war, this vitally needed green corridor has started working," Zelenskyy said Sunday in his nightly address.

A pair of "powerful explosions" were heard early Monday in the western Russian city of Belgorod, about 15 miles from the border with Ukraine, according to the regional governor.

"I woke up to the sound of two powerful explosions half an hour ago. According to the anti-crisis center, there were no reports of casualties or damage. Footage showing flashes in the sky has emerged on social media," Belgorod Oblast Gob. Vyacheslav Gladkov said in a statement posted on Telegram.

The blasts followed a series of other explosions and fires at industrial and military facilities across Russia in recent weeks. On Sunday, the governor of Russia's western Kursk Oblast, which also shares a border with Ukraine, said a railway bridge used to transfer Russian troops to Ukraine had partially collapsed. In a video posted on Telegram, Kurk Oblast Gov. Roman Starovoit blamed the incident on sabotage.

-ABC News' Edward Szekeres, Max Uzol, Irene Hnatiuk and Fidel Pavlenko

Over a quarter of Russian military units committed to fight in Ukraine have been likely rendered "combat ineffective," the U.K. Ministry of Defense said Monday in an intelligence update.

"At the start of the conflict, Russia committed over 120 battalion tactical groups, approximately 65% of its entire ground combat strength," the ministry said. "It is likely that more than a quarter of these units have now been rendered combat ineffective."

Meanwhile, some of Russia's most elite units, including the Russian Airborne Forces or VDV, "have suffered the highest levels of attrition," according to the ministry.

"It will probably take years for Russia to reconstitute these forces," the ministry added.

On Sunday, Ukrainian presidential adviser Oleksiy Arestovych said at least 30 senior Russian military officers have been eliminated in the previous five days.

-ABC News' Edward Szekeres, Max Uzol, Irene Hnatiuk and Fidel Pavlenko

Israel on Monday lashed out at Russia over "unforgivable and scandalous" remarks made by its top diplomat about Nazism and antisemitism, including claims that Adolf Hitler was Jewish.

During an interview Sunday with an Italian television channel, Russian Foreign Minister Sergey Lavrov was asked about Moscow's assertion that it invaded neighboring Ukraine to "denazify" the country. Lavrov said the fact that Ukrainian President Volodymyr Zelenskyy is Jewish does not negate the Nazi elements in his country, drawing a parallel with Hitler, the chancellor of Nazi Germany.

"So when they say: 'How can Nazification exist if we're Jewish?' In my opinion, Hitler also had Jewish origins, so it doesn't mean absolutely anything. For some time we have heard from the Jewish people that the biggest antisemites were Jewish," Lavrov said, speaking to the station in Russian, dubbed over by an Italian translation.

Russia does not insist on Zelenskyy's surrender, Lavrov said, but wants the Ukrainian president to order "neo-Nazi battalions to halt resistance, lay down their arms and let civilian hostages go." Lavrov alleged that Moscow only seeks to guarantee the security of pro-Russia Ukrainians in the eastern regions.

Lavrov's comments came at a time when Israel, which was created as a refuge for Jews in the wake of the Holocaust, has sought to remain neutral amid Russia's war in Ukraine. However, Israeli Foreign Minister Yair Lapid condemned the statement made by his Russian counterpart as "unforgivable and scandalous and a horrible historical error."

"The Jews did not murder themselves in the Holocaust," Lapid, the son of a Holocaust survivor, said Monday. "The lowest level of racism against Jews is to blame Jews themselves for antisemitism."

Ukraine also denounced Lavrov's statement, with Ukrainian Foreign Minister Dmytro Kuleba saying it exposes "the deeply-rooted antisemitism of the Russian elites."

-ABC News' Edward Szekeres, Max Uzol, Irene Hnatiuk and Fidel Pavlenko

Mariupol has not yet fallen, despite Russia's demands that Ukrainian troops defending the besieged Ukrainian port city surrender, according to Ukrainian Prime Minister Denys Shmyhal.

"There [are] still our military forces, our soldiers, so they will fight until the end," Shmyhal told ABC News' George Stephanopoulos in an exclusive interview Sunday on "This Week."

Mariupol is a strategic city for Moscow because it would allow Russian forces in the south to connect with troops in eastern Ukraine's contested Donbas region. It would also give Moscow a key port.

Although Mariupol remains under the Ukrainian government's control, Shmyhal said the city's residents are suffering.

"They have no water, no food, no heat, no electricity," he said. "They ask all of our partners to support and help stop this humanitarian catastrophe."

-ABC News' Monica Dunn