KYIV, Ukraine >> A Russian strike on the Ukrainian city of Zaporizhzhia killed at least 23 people and wounded dozens, an official said Friday, just hours before Moscow planned to annex more of Ukraine in an escalation of the seven-month war.

Zaporizhzhia Regional Governor Oleksandr Starukh made the announcement in an online statement Friday. He said there were at least 28 wounded when Russian forces targeted a humanitarian convoy heading to Russian-occupied territory.

He posted images of burned out vehicles and bodies lying in the road. Russia did not immediately acknowledge the strike.

The attack comes as Moscow prepares to annex four regions into Russia after an internationally criticized, gunpoint referendum vote as part of its invasion of Ukraine. Those regions include areas near Zaporizhzhia, but not the city itself, which remains in Ukrainian hands.

Starukh said those in the convoy planned to travel into Russian-occupied territory to pick up their relatives and then take them to safety. He said rescuers were at the site of the attack.

The annexation — and planned celebratory concerts and rallies in Moscow and the occupied territories — would come just days after voters supposedly approved Moscow-managed “referendums” that Ukrainian and Western officials have denounced as illegal, forced and rigged.

Kremlin spokesman Dmitry Peskov told reporters Thursday that four regions of Ukraine — Luhansk, Donetsk, Kherson and Zaporizhzhia — would be folded into Russia during a Kremlin ceremony attended by President Vladimir Putin, who is expected to give a major speech. Peskov said the regions’ pro-Moscow administrators would sign treaties to join Russia in the Kremlin’s ornate St. George’s Hall.

In an apparent response, Ukrainian President Volodymyr Zelenskyy called an emergency meeting Friday of his National Security and Defense Council.

Zelenskyy also sought to capitalize on anti-war sentiment in Russia by issuing a special video directed at Russia’s ethnic minorities, especially those in Dagestan, one of the country’s poorer regions in the North Caucasus.

“You do not have to die in Ukraine,” he said, wearing a black hoodie that read in English “I’m Ukrainian,” and standing in front of a plaque in Kyiv memorializing what he called a Dagestani hero. He called on the ethnic minorities to resist mobilization.

The U.S. and its allies have promised to adopt even more sanctions than they’ve already levied against Russia and to offer millions of dollars in extra support for Ukraine as the Kremlin duplicates the annexation playbook it followed when it incorporated Ukraine’s Crimean Peninsula in 2014.

Putin early Friday issued decrees recognizing the independence of the Kherson and Zaporizhzhia regions, steps he had taken in February regarding Luhansk and Donetsk and earlier for Crimea.

Ukraine has repeated its vows to recapture the four regions, as well as Crimea. For its part, Russia pledges to defend all its territory — including newly annexed regions — by all available means, including nuclear weapons.

Heightening the tensions are Russia’s partial military mobilization and allegations of sabotage of two Russian pipelines on the Baltic Sea floor that were designed to feed natural gas to Europe. Adding to the Kremlin’s woes are Ukraine’s success in recapturing some of the very land Russia is annexing and problems with the mobilization that President Vladimir Putin acknowledged Thursday.

Ukraine’s Western supporters have described the stage-managed referendums on whether to live under Russian rule as a bald-faced land grab based on lies. They say some people were forced to vote at gunpoint in an election without independent observers on territory from which thousands of residents have fled or been forcibly deported.

In unusually strong language, U.N. Secretary-General Antonio Guterres told reporters Thursday in New York that Russia’s annexation would violate the U.N. Charter and has “no legal value.” He described the move as “a dangerous escalation” and said it “must not be accepted.”

“Any decision by Russia to go forward will further jeopardize the prospects for peace,” Guterres said.

As a veto-wielding permanent member of the U.N. Security Council, Russia bears “a particular responsibility” to respect the U.N. Charter, the secretary-general said.

U.N. spokesman Stephane Dujarric said Guterres conveyed the message to Russia’s U.N. ambassador, Vassily Nebenzia, on Wednesday.

In what would be a major blow to Moscow’s war effort, the Washington-based Institute for the Study of War said Ukrainian forces may soon encircle Lyman, 160 kilometers (100 miles) southeast of Kharkiv, Ukraine’s second-largest city.

“The collapse of the Lyman pocket will likely be highly consequential to the Russian grouping” in the northern Donetsk and western Luhansk regions and “may allow Ukrainian troops to threaten Russian positions along the western Luhansk” region, the institute said, citing Russian reports.

Andrew Katell in New York and Edith M. Lederer at the United Nations contributed to this report.