Pro-Russia authorities in the eastern Donetsk and Luhansk regions, as well as in the southern Kherson and Zaporizhzhia regions, say they will hold separatist votes over five days beginning Friday this week.
A section of world leaders meeting at the United Nations in New York has criticised Russia's offensive in Ukraine, with Moscow-appointed leaders in occupied areas of four Ukrainian regions announcing plans to hold referendums on joining Russia.
In the apparently coordinated move on Tuesday, pro-Russian figures announced referendums for September 23-27 in Luhansk, Donetsk, Kherson and Zaporizhzhia provinces, representing around 15% of Ukrainian territory, or an area about the size of Hungary.
"The Russians can do whatever they want. It will not change anything," Ukraine's Foreign Minister Dmytro Kuleba said on Tuesday, in response to reporters' questions at the UN, where leaders were gathering for a General Assembly meeting.
If the referendum plan "wasn't so tragic it would be funny," French President Emmanuel Macron told reporters ahead of the UN assembly in New York.
Japanese Prime Minister Fumio Kishida told the assembly the UN's credibility was in danger because of the aggression by Russia, a permanent member of the Security Council, and reforms of the UNSC were needed.
"Russia's invasion of Ukraine is a conduct that tramples the philosophy and principles of the UN charter...It should never be tolerated," Kishida said.
Sham ‘referendums’ will not change anything. Neither will any hybrid ‘mobilization’. Russia has been and remains an aggressor illegally occupying parts of Ukrainian land. Ukraine has every right to liberate its territories and will keep liberating them whatever Russia has to say.— Dmytro Kuleba (@DmytroKuleba) September 20, 2022
Some pro-Kremlin figures framed the referendums for those four regions as an ultimatum to the West to accept Russian territorial gains or face an all-out war with a nuclear-armed foe.
"Encroachment onto Russian territory is a crime which allows you to use all the forces of self–defence," Dmitry Medvedev, a former Russian president and now deputy chairperson of Putin's Security Council, said on social media.
Reframing the fighting in occupied territory as an attack on Russia could give Moscow a justification to mobilise its 2 million-strong military reserves. Moscow has so far resisted such a move despite mounting losses.
US National Security Adviser Jake Sullivan said Washington was aware of reports Putin might be considering ordering a mobilisation. That would do nothing to undermine Ukraine's ability to push back Russian aggression, Sullivan said, adding that Washington rejected any such referendums "unequivocally".
Russia already considers Luhansk and Donetsk, which together make up the eastern Donbass region Moscow partially occupied in 2014, to be independent states. Ukraine and the West consider all parts of Ukraine held by Russian forces to be illegally occupied.
Russia now holds about 60% of Donetsk and had captured nearly all of Luhansk by July after slow advances during months of intense fighting.
Those gains are now under threat after Russian forces were driven from neighbouring Kharkiv province this month, losing control of their main supply lines for much of the Donetsk and Luhansk front lines.
"The situation on at the front clearly indicates the initiative is with Ukraine," Ukrainian President Volodymyr Zelenskyy said in a video address released early on Wednesday.
Ukraine's position did not change because of "some noise" from Russia, Zelenskyy added in a reference to the referendums.
In Kherson, where the regional capital is the only major city Russia has so far captured intact since its offensive, Ukraine has launched a major counter-offensive.
In the south, Russia controls most of Zaporizhzhia but not its regional capital.
Vladimir Rogov, a Russian-appointed official in Zaporizhzhia, said becoming part of Russia would help solve the conflict more quickly.
"This will show people with full clarity that Russia is here to stay, forever," he said on Telegram. "And they will take the necessary decision more quickly, lay down their weapons and cross over to the side of their people, their countrymen."