KYIV, Ukraine--Russian-controlled regions of eastern and southern Ukraine announced plans Tuesday to start voting this week to become integral parts of Russia. The Kremlin-backed efforts to swallow up four regions could set the stage for Moscow to escalate the war following Ukrainian successes on the battlefield.

The scheduling of referendums starting Friday in the Luhansk, Kherson and partly Russian-controlled Zaporizhzhia and Donetsk regions came after a close ally of Russian President Vladimir Putin said the votes are needed and as Moscow is losing ground in the invasion it began nearly seven months ago.

Former President Dmitry Medvedev, the deputy head of Russia’s Security Council chaired by Putin, said referendums that fold regions into Russia itself would make redrawn frontiers “irreversible” and enable Moscow to use “any means” to defend them.

In 2014, Russia sent troops into Ukraine’s Crimean Peninsula and then held a referendum there that paved the way for its annexation by Moscow.

The upcoming votes, in territory Russia already controls, are all but certain to go Moscow’s way. But they were quickly dismissed as illegitimate by Western leaders who are backing Kyiv with military and other support that has helped its forces seize momentum on battlefields in the east and south.

Ukrainian Foreign Minister Dmytro Kuleba denounced the planned votes as a sham.

“The referendums will change nothing,” he told reporters at U.N. headquarters where he is attending the General Assembly’s annual gathering of world leaders. “It’s an act of desperation for Russia, but it is not going to help them.”

U.S. national security adviser Jake Sullivan said the United States would "never recognize this territory as anything other than part of Ukraine," he said, adding that the Kremlin effort reflects Russia's setbacks on the battlefield.

“These are not the actions of a confident country. These are not acts of strength," he said.

German Chancellor Olaf Scholz, who is also attending the U.N. General Assembly in New York, said: “It is very, very clear that these sham referendums cannot be accepted.”

French President Emmanuel Macron said referendum plans amounted to “cynicism.”

“Russia declared war ... and now it explains that in this same region it is going to organize a referendum. If this were not tragic, it might be funny,” he said, adding that the votes would have “no legal consequences.”

Authorities installed by Russia in occupied areas of four Ukrainian regions had outlined plans to hold referendums on membership to the Russian Federation later this month. They have been condemned by Ukraine.

Latvian Foreign Minister Edgars Rinkevics called for more sanctions against Russia and more weapons for Ukraine, tweeting: “We must say no to Russian blackmail.”

In Donetsk, part of Ukraine's wider Donbas region that Putin has set as a primary objective of the invasion, separatist leader Denis Pushilin said the vote will “restore historic justice" to the territory's “long-suffering people."

They “have earned the right to be part of the great country that they always considered their motherland,” he said.

In partly Russian-occupied Zaporizhzhia, pro-Russia activist Vladimir Rogov said: “The faster we become part of Russia, the sooner peace will come.”

Pressure inside Russia for votes and from Moscow-backed leaders in Ukrainian regions that Moscow controls increased after a Ukrainian counteroffensive that has recaptured large areas.

Former Kremlin speechwriter and Russian political analyst Abbas Gallyamov said on Facebook that Moscow-backed separatists appeared “scared that the Russians will abandon them” amid the Ukrainian offensive and forged ahead with referendum plans to force the Kremlin's hand.

In another signal that Russia is digging in for a protracted and possibly ramped-up conflict, the Kremlin-controlled lower of house of parliament voted Tuesday to toughen laws against desertion, surrender and looting by Russian troops. Lawmakers also voted to introduce possible 10-year prison terms for soldiers refusing to fight.

If approved, as expected, by the upper house and then signed by Putin, the legislation would strengthen commanders’ hands against failing morale reported among soldiers.

In an interview in New York with the “PBS News Hour,” Turkish President Recep Tayyip Erdogan said that if peace is to prevail in Ukraine, "the returning of the land that was invaded will become really important.”

He also repeated his long-held position that the Crimean Peninsula should be returned to Ukraine. Turkey has strong ethnic ties to Crimean Tatars. “Since 2014, we have been talking to my dear friend Putin about this, and this is what we have requested from him,” he said.

In the Russian-occupied city of Enerhodar, shelling Tuesday around Europe's largest nuclear power plant damaged a cooling system, a dining hall for staff and an unspecified “special building," the city administration said in a statement. There were no further details about the damage.

The Zaporizhzhia Nuclear Power Plant has been a focus for concern for months because of fears that shelling could lead to a radiation leak. Russia and Ukraine blame each other for the shelling.

Kremlin spokesman Dmitry Peskov said there are no prospects for a diplomatic settlement of the conflict. Medvedev, who served as Russia’s president from 2008 to 2012, said on his messaging app channel that the referendums are important to protect their residents and would "completely change" Russia's future trajectory.

“After they are held and the new territories are taken into Russia’s fold, a geopolitical transformation of the world will become irreversible," Medvedev said.

“An encroachment on the territory of Russia is a crime that would warrant any means of self-defense,” he said, adding that Russia would enshrine the new territories in its constitution so no future Russian leader could hand them back.

“That is why they fear those referendums so much in Kyiv and in the West,” Medvedev said. “That is why they must be held.”

Ukrainian analyst Volodymyr Fesenko, head of the independent Penta Center think tank in Kyiv, said the Kremlin hopes the votes and the possibility of military escalation will raise the pressure from Western governments for Ukrainian President Volodymyr Zelenskyy to start talks with Moscow.

The move “reflects the weakness, not the strength of the Kremlin, which is struggling to find levers to influence the situation that has increasingly spun out of its control,” he said.

The recapturing of territory, most notably in the northeastern Kharkiv region, has strengthened Ukraine's arguments that its troops could deliver more stinging defeats to Russia with additional armament deliveries.

More heavy weaponry is on its way, with Slovenia promising 28 tanks and Germany pledging four additional self-propelled howitzers. More aid also is expected from Britain, already one of Ukraine's biggest military backers after the U.S. British Prime Minister Liz Truss is expected to promise that in 2023, her government will “match or exceed” the 2.3 billion pounds ($2.7 billion) in military aid given to Ukraine this year.

The swiftness of the Ukrainian counteroffensive also saw Russian forces abandon armored vehicles and other weapons as they beat hasty retreats. Ukrainian forces are recycling the captured weaponry back into battle. A Washington-based think tank, The Institute for the Study of War, said abandoned Russian T-72 tanks are being used by Ukrainian forces seeking to push into Russian-occupied Luhansk.

In the counteroffensive's wake, Ukrainian officials found hundreds of graves near the once-occupied city of Izium. Yevhenii Yenin, a deputy minister in Ukraine’s Internal Affairs Ministry, told a national telecast that officials found many bodies “with signs of violent death."

“These are broken ribs and broken heads, men with bound hands, broken jaws and severed genitalia,” he said.

Prosecutor-General Andriy Kostin, during a trip to Washington, said Tuesday that another mass grave with possibly 100 bodies was discovered in another village in the counteroffensive area.

Meanwhile, Ukraine’s southern military command said its troops sank a Russian barge carrying troops and weapons across the Dnieper River near the Russian-occupied city of Nova Kakhovka. It offered no other details on the attack in the Russian-occupied Kherson region, which has been a major target in the Ukrainian counteroffensive.