KYIV, Ukraine (AP) - Russia planned to annex more of Ukraine on Friday in an escalation of the seven-month war that was expected to isolate the Kremlin further, draw it more international punishment and bring Ukraine extra military, political and economic support.

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.

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.

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 is 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, during a meeting Wednesday.

The European Union also objected strongly to Russia's plans.

“It's absolutely unacceptable,” said Czech Foreign Minister Jan Lipavsky, whose country holds the European Union presidency. “We reject such one-sided annexation based on a fully falsified process with no legitimacy.”

Lipavsky described the pro-Russia referendums as “theater play” and insisted the regions remain “Ukrainian territory.”

German Foreign Minister Annalena Baerbock said at a conference in Berlin that Russia's moves were “the opposite of peace.”

“It's dictated peace. As long as this Russian diktat prevails in the occupied territories of Ukraine, no citizen is safe. No citizen is free,” he said.

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 entirely encircle Lyman, a city 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.

Elsewhere on the battlefront, rescuers pulled a sleeping 12-year-old girl out alive from rubble after a Russian missile attack on Dnipro, local administrator Valentyn Reznichenko said.

Moscow-installed officials in Ukraine's northeastern Kharkiv region reported that about 30 people were killed when the Ukrainian military shelled a refugee convoy on Thursday. The claim could not be independently verified.

A Russian rocket attack on Kramatorsk, an eastern Donetsk city that Ukraine still holds, wounded 11 people and inflicted damage, Mayor Oleksandr Honcharenko said.

More fighting near the Zaporizhzhia Nuclear Power Plant - Europe's biggest - was another source of concern. Russian forces occupy the plant, but Ukrainian technicians still are running it.

A suspected land mine explosion Thursday on the power plant's perimeter fence was likely triggered by wild animals. The blast damaged electrical lines, according to Ukraine's atomic power agency, Energoatom.

Russia's partial mobilization has been chaotic and unpopular, triggering protests and violence. Russian men have formed miles-long lines trying to leave the country, and Moscow reportedly set up draft offices at its borders to intercept some of those fleeing.

In an apparent effort to calm the population, Putin told Russia's Security Council on Thursday that mistakes had been made in the mobilization, that Russian men mistakenly called up should be sent home and that only reservists with proper training and specialties should be summoned to serve.

Multiple reports have surfaced of Russian men outside the eligible categories being forced to serve, and of reservists being provided inadequate training and equipment.

British military intelligence claimed the number of Russian military-age men fleeing the country likely exceeds the number of forces that Moscow used to initially invade Ukraine in February.

“The better off and well educated are over-represented amongst those attempting to leave Russia,” the British said.

They warned that economic effects from the reduced availability of labor “and the acceleration of `brain drain”' are “likely to become increasingly significant.”

On the subject of sabotage that hit Russian gas pipelines to Europe this week, Peskov claimed Thursday that the Nord Stream pipeline accidents would have been impossible without a government's involvement.

“It looks like a terror attack, probably conducted on a state level,” Peskov told reporters. “It's a very dangerous situation that requires a quick investigation.”

He dismissed media reports about Russian warships detected in the area as “stupid and biased,” claiming that many more NATO aircraft and ships “have been spotted” there.

NATO warned Thursday that it would retaliate for any attacks on the critical infrastructure of its 30 member countries and joined other Western officials in citing sabotage as the likely cause of the pipeline damage.

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