NEW YORK, Sept 21 ― World leaders meeting at the United Nations in New York denounced Russia's invasion of Ukraine, as Moscow-installed leaders in occupied areas of four Ukrainian regions announced plans to hold referendums on joining Russia in coming days.

In the apparently coordinated move, pro-Russian figures announced referendums for September 23-27 in Luhansk, Donetsk, Kherson and Zaporizhzhia provinces, representing around 15 per cent 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 United Nations where leaders were arriving for a General Assembly meeting likely to be dominated by the war in Ukraine.

In a tweet, he added: "Ukraine has every right to liberate its territories and will keep liberating them whatever Russia has to say.”

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.

Russian President Vladimir Putin on February 24 ordered what he calls a "special military operation” in Ukraine to root out dangerous nationalists and "denazify” the country. The war has killed thousands, destroyed cities and sent millions fleeing their homes in the former Soviet republic.

German Chancellor Olaf Scholz said Putin will only give up his "imperial ambitions” that risk destroying Ukraine and Russia if he recognises he cannot win the war.

"This is why we will not accept any peace dictated by Russia and this is why Ukraine must be able to fend off Russia's attack,” Scholz said in his first address to the General Assembly.

Japanese Prime Minister Fumio Kishida told the assembly the UN's credibility was in danger because of the invasion by Russia, a permament 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 U.N. charter ... It should never be tolerated,” Kishida said.

Justification to mobilise

Some pro-Kremlin figures framed the referendums for occupied 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 hawkish deputy chairman 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 Donbas 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 per cent 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.

‘Some noise’

"The situation on at the front clearly indicates the initiative is with Ukraine,” Ukrainian President Volodymyr Zelensky said in a video address released early on Wednesday.

Ukraine's position did not change because of "some noise” from Russia, Zelensky 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 the invasion, 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.” ― Reuters