KYIV, Ukraine (AP) — Russian-controlled regions of eastern and southern Ukraine announced plans Tuesday to start voting this week to become integral parts of Russia. The concerted and quickening 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, increasing pressure on the Kremlin for a stiff response.

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.

Ukrainian Foreign Minister Dmytro Kuleba denounced the votes as a sham and tweeted that "Ukraine has every right to liberate its territories and will keep liberating them whatever Russia has to say."

The votes, in territory Russia already controls, are all but certain to go Moscow's way but are unlikely to be recognised by Western governments who are backing Ukraine with military and other support that has helped its forces seize momentum on battlefields in the east and south.

In Donetsk, part of Ukraine's wider Donbas region that has been gripped by rebel fighting since 2014 and which 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."