Ukraine Accuses Russia of Digging Mass Graves for Civilian Victims

Maj. Gen. Rustam Minnekayev, deputy commander of Russia’s Central Military District, said in remarks at a conference carried by state media on Friday that Moscow sought to control all of southern Ukraine to secure a land corridor to Crimea, the Ukrainian peninsula that Moscow annexed in 2014, and to Moldova’s Transnistria region, where he said Russian speakers suffer from discrimination.

To achieve these goals, Russia, in addition to capturing the parts of Donbas that remain under Ukrainian control, would also have to seize the coastal regions of Mykolaiv and Odessa. Russian forces came close to overrunning Mykolaiv in early March, but since have been repelled and control a sliver of the region.

Moscow, however, occupies most of the Kherson region in southern Ukraine and a large part of the Zaporizhzhia region. Russia’s RIA state news agency Friday ran interviews with a member of the Russian parliament, Dmitriy Belik, and a pro-Moscow Crimean Tatar leader, Eyvaz Umerov, calling for absorbing these occupied territories into a new Crimean federal district within Russia.

Kremlin spokesman

Dmitry Peskov

declined to comment on the possibility of Russia expanding its military aims in southern Ukraine. It wasn’t clear to what extent Gen. Minnekayev’s remarks—which also included the false claims that Russia fought “against the entire world” in World War II and that Russian armed forces are suffering no casualties in Ukraine—reflected the Kremlin’s policy.

In Mariupol—much of which has been leveled by shelling, bombing and street fights—Ukrainian municipal authorities said mass graves for residents killed by the Russian army were being dug outside the city in an area that is already twice as large as the local cemetery.

“The worst war crime of the 21st century has been committed in Mariupol,” Mayor

Vadym Boychenko

said in remarks posted by the municipality on social media. “Putin is exterminating Ukrainians. He has already killed tens of thousands of civilians in Mariupol.”

Satellite images released Thursday by

Maxar Technologies

showed what appeared to be more than 200 mass graves in the town of Manhush, just outside Mariupol. These graves could contain between 3,000 and 9,000 people, the municipality said. Russia didn’t immediately respond to a request for comment. In general it ascribes all civilian casualties in Mariupol to Ukrainian forces.

Russia on Thursday announced a victory in the strategic port city even though Ukrainian forces were still blockaded inside its vast Azovstal steel plant. A spokesman for Ukrainian President

Volodymyr Zelensky

said while nearly all of Mariupol was under Russian control, the fight for the plant continued.

A rare acknowledgment of Moscow’s deliberate strategy to level Mariupol, which used to be home to about 400,000 people, came from a Thursday address by Adam Delimkhanov, a Russian lawmaker from Chechnya who led Chechen units of the Russian National Guard in battles for the city.

“We can say that the special operation to destroy and cleanse Mariupol has now been concluded,” Mr. Delimkhanov said alongside a unit of Chechen Russian National Guard troops in front of a burning Mariupol building. The troops in the video chanted, “Russia is strength” and “Allahu akbar.”

Mr. Peskov said Russian troops had sealed off the Azovstal steel plant, where an estimated 1,500 Ukrainian troops were holed up. Ukrainian soldiers in Mariupol said they would be ready to withdraw with their arms if their safety were guaranteed by a third party.

British Prime Minister

Boris Johnson

on Friday said he agreed with a Western intelligence assessment that the war in Ukraine could continue until the end of next year and that Russia could win.

“I think the sad thing is it is a realistic possibility,” Mr. Johnson said. “Putin has a huge army, he has a very difficult position because he’s made a catastrophic blunder—the only option he has now is to continue to try to use his appalling, grinding approach.”

The British government also said it would reopen its embassy in Kyiv next week, joining a host of nations returning to the Ukrainian capital after Russian forces pulled back from Kyiv and other cities in the north. And Mr. Johnson said the government proposes sending tanks to Poland.

The U.S. doesn’t have diplomatic personnel in Ukraine and hasn’t outlined any plans for American diplomats to return.

As part of an effort to pursue an end to the war, United Nations Secretary-General

António Guterres

will travel to Moscow and meet with Mr. Putin and Russian Foreign Minister Sergei Lavrov on Tuesday and will travel to Ukraine and meet with Mr. Zelensky and Ukrainian Foreign Minister

Dmytro Kuleba

on Thursday, according to Mr. Guterres’s office.

Mr. Putin ordered Russian forces to focus on seizing the parts of Donbas that remain under Ukrainian control, after his initial plan to swiftly conquer the capital, Kyiv, and other major cities of eastern and central Ukraine failed because of fierce resistance. Russia’s new strategy, Ukrainian and Western officials say, is to encircle Ukraine’s best forces in Donbas through a pincer movement, with offensives pushing north from the Zaporizhzhia region and south from the town of Izyum.

So far, Russian forces have made incremental gains, taking a handful of small villages since seizing the town of Kreminna last weekend. Russian forces on Friday pushed toward Slovyansk, one of the main cities in Ukrainian-controlled Donbas, and took over the village of Lozove, according to Ukraine’s general staff.

Ukraine’s military has been able to curtail Russia’s overwhelming advantage in aircraft by using Western-supplied antiaircraft missiles, such as Stinger and Starstreak, to down several Russian jet fighters, helicopters and drones in recent days, according to footage of wreckage posted by Ukrainian troops and verified by military analysts. Ukraine said Friday it lost an An-26B transport plane that hit a power line in the Zaporizhzhia region, leaving at least one crew member dead.

With the battle for Donbas pitting conventional forces against each other, Ukraine is struggling to make up for its disadvantage in artillery and its shortage of Soviet-standard ammunition—one reason why Mr. Zelensky has repeatedly asked the U.S. and allies to supply NATO-standard heavy weapons.

The U.S. has been the first to provide Ukraine with NATO-standard 155-mm howitzers. President Biden said Thursday that Washington’s latest $800 million military-aid package would include 72 of these towed artillery pieces in addition to 18 pledged the previous week.

On Friday, Canada said its military also sent an unspecified number of 155-mm howitzers and anti-armor ammunition to Ukraine. Canadian Broadcasting Corp., citing a military source, reported the package would include GPS-guided Excalibur rounds, which are valued at about $112,000 per round.

In an interview published Friday by newspaper Ouest-France, French President

Emmanuel Macron

said Paris is providing Ukraine with Caesar self-propelled 155-mm artillery pieces. The newspaper, citing military sources, reported that Paris was transferring 12 Caesars, which have a range of some 40 kilometers, equivalent to about 25 miles, and that Ukrainian soldiers would begin training Saturday in France.

Ukrainian officials have warned recently that Moscow plans in the coming weeks to conduct a sham referendum on severing Russian-controlled parts of Zaporizhzhia and Kherson from Ukraine and possibly proclaiming a so-called Kherson people’s republic, similar to what it did in Crimea, Donetsk and Luhansk in 2014. That would allow Russia to start forcibly drafting local men, as has happened with the mandatory mobilization of men up to 65 years old in Donetsk and Luhansk.

Russia already has replaced most mayors in occupied areas of southern Ukraine with handpicked allies, with the exception of the mayor of the city of Kherson. Moscow hasn’t commented publicly on referendum plans. “Not a single person in the Kherson region, which awaits liberation, will come to that referendum,” the Ukrainian governor of Kherson, Hennadiy Lahuta, said in a TV appearance. “Anything they may conduct will be unlawful and falsified.”

—Georgi Kantchev contributed to this article.

Write to Yaroslav Trofimov at yaroslav.trofimov@wsj.com