A Russian rocket strike hit a strategically important bridge across the Dniester estuary in the Odessa region of southwestern Ukraine, a local official said.

The bridge, which Russian forces have already struck twice, is the only road and rail link on Ukrainian territory to the southwestern part of the Odessa region from its capital.

The Odessa regional administration’s spokesman, Serhoy Bratchuk, gave no further details in reporting the strike on social media on Monday.

Russia on Saturday knocked out the runway of Odessa’s airport with a missile strike, part of an uptick in violence in a region that Moscow has designs on. Ukraine said it had destroyed two Russian boats in strikes of its own Monday with a drone.

Nearby Moldova placed its security forces on alert last month after a series of explosions in Transnistria, a pro-Russian breakaway enclave where some 1,500 Russian troops are stationed.

However, the chance of a Russian assault in the region in the near future appears slim, analysts say, as Russian land forces have been pushed back from the strategic city of Mykolaiv in Ukraine’s south.

A handout photo from Finnish nuclear power company Fennovoima shows an illustration of the nuclear plant by Russia’s atomic energy corporation, Rosatom, that was planned for the Hanhikivi site, Pyhäjoki, Finland.Agence France-Presse/Getty Images

A Finnish consortium has rescinded a contract to build a nuclear power plant with Russian state-owned nuclear enterprise Rosatom, citing its inability to deliver the project after Moscow’s invasion of Ukraine.

“There have been significant and growing delays during the last years. The war in Ukraine has worsened the risks for the project,” Fennovoima Oy, a consortium that includes Finnish state-owned power and industrial companies, said in a statement on Monday.

Fennovoima warned last month that it expected Western-backed sanctions against Russia to affect the Hanhikivi 1 nuclear project, although it couldn’t provide a detailed assessment of the impact.

Rosatom, which owns a 34% stake in the consortium through its Finnish subsidiary RAOS Voima Oy, called the decision to cancel the contract disappointing, saying the reasons behind it were incomprehensible.

Finland had approved the controversial Russian-backed project in 2014, strengthening energy ties between Helsinki and Moscow at a time when many Western capitals were seeking to isolate Russia over its annexation of Crimea in the same year.

Mika Lintilä, Finland’s minister of economic affairs, on Monday wrote on Twitter that it would have been virtually impossible to take the project forward.

Fennovoima was hoping to obtain a construction license for the project this year. The nuclear plant, with estimated costs ranging from roughly $7.4 billion to $7.9 billion, was meant to cover about 10% of Finland’s electricity needs, according to the consortium.

Russian Foreign Minister Sergei Lavrov.Yuri Kochetkov/Associated Press

Russian Foreign Minister Sergei Lavrov compared Ukrainian President Volodymyr Zelensky, who is Jewish, to Hitler and accused Jews of anti-Semitism.

Israeli Foreign Minister Yair Lapid on Sunday called Mr. Lavrov’s comments “a terrible historical error” and said he was summoning Russia’s ambassador for consultations and would demand an apology.

Asked Sunday by Italy’s Rete 4 channel about Russian claims that it invaded Ukraine to “denazify” the country, Mr. Lavrov said that Ukraine could still have Nazi elements even if some figures, including Zelensky, were Jewish.

“When they say, ‘What sort of Nazification is this if we are Jews’—well I think that Hitler also had Jewish origins, so it means nothing,” Mr. Lavrov said, speaking through an interpreter.

He added: “For a long time now we’ve been hearing the wise Jewish people say that the biggest anti-Semites are the Jews themselves.”

Russian officials have repeatedly claimed that one of their aims in attacking Ukraine was to remove Nazi elements from its government.

Russian President Vladimir Putin has said the invasion of Ukraine is justified because the country’s leaders are nationalists and neo-Nazis who must be stopped from carrying out a genocide against Russians and Russian-speaking citizens of Ukraine. He has provided no evidence for the claims.

Mr. Lavrov appeared to amplify a conspiracy theory that Hitler’s paternal grandfather was Jewish, which was first popularized by the 1953 memoir by Hitler’s lawyer Hans Frank, who claimed to have found evidence of the Nazi leader’s alleged Jewish ancestry.

These claims have been dismissed by mainstream historians.

In the Soviet Union, and later in Russia, the terms “Nazi” and “fascist” have been frequently used to smear all opponents, including opposition activists and foreign critics.

Two explosions rocked the southern Russian region of Belgorod in the early hours of Monday, the region’s governor said.

“I woke up 30 minutes ago from two strong blasts,” Vyacheslav Gladkov wrote on his Telegram messenger channel, adding that there weren’t any casualties or damage from the explosions.

Mr. Gladkov later posted that the explosions had been caused by Russian aircraft carrying a combat mission and that the safety of residents was never at threat.

On Sunday, Mr. Gladkov said a fire had broken out at a Ministry of Defense facility in the region. One person had been wounded and seven houses damaged in the incident, he said.

Russia has accused Ukraine of sporadic attacks and acts of sabotage on its territory in recent weeks. Kyiv has either denied responsibility or declined to comment on the accusations.

On Sunday, Roman Starovoit, the regional governor of Russia’s Kursk region, said the partial collapse of a railway bridge was an act of sabotage.

“Specialists from law-enforcement agencies will investigate in more detail,” Mr. Starovoit said on Telegram, adding that there were no casualties.

The Russian Defense Ministry didn’t immediately comment on the incident.

There were at least two other explosions in recent days and a fire on Sunday at an oil depot in the Russian city of Bryansk, also close to the Ukraine border.

Polish President Andrzej Duda, left, next to U.S. House of Representatives Speaker Nancy Pelosi in Warsaw, Poland, on Monday.andrzej lange/Shutterstock

House Speaker Nancy Pelosi said the U.S. and its European allies would continue to work on strengthening the North Atlantic Treaty Organization as she led a delegation of U.S. lawmakers to Poland after visiting Ukraine.

After meeting Polish President Andrzej Duda, Mrs. Pelosi said the U.S. was grateful for Poland opening its doors to millions of refugees from Ukraine since Russia’s invasion of the country in late February.

“We reaffirmed our nation’s pledge to continue supporting Poland’s humanitarian efforts,” she said in a statement. “Our Members discussed our countries’ continued commitment to Ukraine, particularly as the Congress prepares to transform President Biden’s new request for additional security, economic and humanitarian assistance into legislation.”

“Our meeting also focused on reaffirming our nations’ joint commitment to further strengthening the U.S.-Polish partnership and the NATO alliance,” she added, saying both were “vital to ensuring the triumph of our common democratic values and countering Putin’s dangerous aggression.”

Mrs. Pelosi and the delegation met with Ukrainian President Volodymyr Zelensky on Saturday night and reiterated Washington’s pledge to keep supporting Ukraine until it secured a victory against Russia.

South Korea said it had returned its ambassador to Ukraine and some staff to the country’s embassy in Kyiv to begin work Monday.

In mid-February, South Korea evacuated its Kyiv embassy. The ambassador and returning staff since March had worked in a temporary office in the western Ukrainian city of Chernivtsi, Seoul’s foreign ministry said in a Sunday statement. It is considering a phased return to the Kyiv embassy in accordance with the security situation, the foreign ministry said.

The ambassador to Ukraine, Kim Hyung-tae, and other embassy workers had arrived Saturday in Kyiv. More than 20 embassies have returned in some form to the Ukrainian capital, South Korea’s foreign ministry said.

South Korea recently said it plans to make an additional donation to Ukraine for nonlethal military supplies, such as fuel or protective gear, of roughly $50 million. The money will be provided through a trust fund of the North Atlantic Treaty Organization, South Korea’s foreign ministry said last week.

A fire following Russian shelling in Kharkiv, Ukraine, on Saturday.RICARDO MORAES/REUTERS

New Zealand said it is adding dozens of Russian politicians and several defense companies to its sanctions list over Moscow’s invasion of Ukraine.

The government said Monday that its latest round of sanctions targets 170 members of Russia’s parliament as well as six companies in the defense sector that New Zealand says contributed to Moscow’s offensive against Ukraine.

The move is the latest by the island nation to target Moscow’s elites through measures that have so far included travel bans and asset freezes. More than 400 Russians have now been sanctioned by New Zealand.

“As President Putin’s war machine continues its illegal attacks and as further revelations of atrocities come to light, we are determined to impose costs on those involved,” New Zealand Foreign Minister Nanaia Mahuta said.

“We support the people of Ukraine, and we are committed to holding President Putin and his cadre of warmongers to account,” she added.

Last month New Zealand restricted dealings with 18 Russian financial institutions, including the country’s central bank and sovereign wealth fund.

New Zealand already froze the assets of President Vladimir Putin, members of Russia’s Security Council, as well as other political, economic and military elites. It is also applying a 35% tariff on all Russian imports.

A Ukrainian refugee after crossing the Ukrainian-Moldovan border into Moldova in mid April.christophe archambault/Agence France-Presse/Getty Images

The number of people fleeing Ukraine since the start of Russia’s invasion at the end of February crossed 5.5 million on Monday, according to the United Nations refugee agency.

The U.N. High Commissioner for Refugees said that 5.56 million people have left Ukraine since Feb. 24, the largest movement of people in Europe since World War II.

UNHCR now estimates that some 8.3 million people will flee the country as a result of the war, more than double its initial estimate at the outset of the conflict.

Some three million refugees have made their way to Poland, which shares a more-than 300-mile border with Ukraine. Visa-free travel within the European Union makes it difficult to know how many have remained in Poland or moved on to other countries.

The Ukraine Border Patrol said 1.36 million people have crossed frontiers into Ukraine since the start of the war, but that number also captures people going back and forth across the border.