President Vladimir Putin formally incorporated four partially-occupied Ukrainian regions into Russia on Wednesday, a move Kyiv condemned as a meaningless land grab dreamt up by “a collective madhouse”.

Pushing ahead with Europe’s biggest annexation since World War Two, Putin signed off on a law annexing up to 18 per cent of Ukraine, some of which Moscow’s forces do not control.

Including Crimea, which Russia annexed in 2014, Moscow is laying claim to almost a quarter of Ukraine, though it has yet to spell out where all of the borders will be located and its own troops have been forced to retreat on two fronts.

The Russian leader’s signature was the final stage in the legal process to annex Donetsk and Luhansk in eastern Ukraine and Zaporizhzhia and Kherson in the south. He later said Russia would stabilise the situation there, an indirect acknowledgement of the challenges it faces to assert its control.

Kyiv says it will never accept an illegal imperial-style land grab and has recaptured hundreds of square miles of its own territory in recent weeks.

Andriy Yermak, head of Ukraine’s presidential office, said on Telegram that what Russia was doing reminded him of a “collective madhouse”.

“Worthless decisions by a terrorist country are not worth the paper they are signed on,” he said.

With even Russian state TV hosts showing signs of despondency at the battlefield losses, Kremlin spokesman Dmitry Peskov dismissed the idea that they undermined the annexation of the regions.

“They will be with Russia forever and they (ceded land in the new territories) will be returned”, a defiant Peskov told reporters.

A map published by the state RIA news agency suggested Russia wants big chunks of Ukraine under the control of the Ukrainian army which has been rapidly advancing in the east, and which this week made a breakthrough in the south too.

Kyiv and its Western allies say Russia’s attempted annexation is an illegal land grab and will never be recognised with Ukraine saying its army will recapture any territory occupied by Russian forces.

The European Union agreed to a new package of sanctions on Wednesday to punish Russia for the annexation plan. The measures include more restrictions on trade with Russia in steel and tech products, and an oil price cap for Russian seaborne crude deliveries through European insurers to align the bloc with Washington.

Ukrainian President Volodymyr Zelenskiy said on Tuesday night that his military had made major, rapid advances against Russian forces in the past week, taking back dozens of towns in regions in the south and east that Russia has declared annexed.

“This week alone, since the Russian pseudo-referendum, dozens of population centres have been liberated. These are in Kherson, Kharkiv, Luhansk and Donetsk regions altogether,” Zelenskiy said.

Zelenskiy named eight small towns in Kherson in the south as recently having been recaptured. Reuters could not independently verify his statements.

Russians dig in

Russian forces in the Donetsk and Kherson regions, who have been forced to retreat in recent days, have dug in at new positions where they hope to halt the Ukrainian advance.

Moscow moved to annex those regions after holding what it called referendums over several days from September 23 — votes that were denounced by Kyiv and Western governments as illegal and coercive.

A video released by the Ukraine defence ministry on Tuesday appeared to show the Ukrainian flag being raised over one of those communities, Davydiv Brid, in Kherson.

Russian defence ministry maps presented on Tuesday also appeared to show rapid withdrawals of Russian forces from areas in eastern and southern Ukraine where they have been under severe pressure from the Ukrainian counteroffensive.

In the east, Ukrainian forces have been expanding an offensive after capturing the main Russian bastion in the north of Donetsk, the town of Lyman.

“In some areas of the front line it was possible to extend the area we hold from between 10 to 20 kilometres,” the southern Operational Command of the Ukrainian Armed Forces (UAF) said on Wednesday.

Russian forces were destroying their reserves of ammunition and trying to destroy bridges and crossings in order to slow the Ukrainian advance, the UAF said in its daily report.

In Kherson, withdrawing Russian forces were planting mines on “infrastructure facilities” and in homes, it said.

In the past 24 hours, Russia had lost 31 servicemen and more than 40 pieces of equipment, including eight tanks, 26 armoured vehicles, and a large calibre howitzer, it said.

Moscow hopes a “partial mobilisation” it announced two weeks ago can help reverse a series of battlefield setbacks with some officials saying they intend to retake territory ceded to Ukraine.

Defence Minister Sergei Shoigu was cited by the RIA news agency on Tuesday as saying that Russia had so far called up more than 200,000 reservists out of a planned 300,000 men.

Many Russian men have fled the country rather than fight in Ukraine, however, and Russian lawyers say they are working flat out to advise men who want to avoid being drafted.

In a boost for Ukraine, US President Joe Biden told Zelenskiy in a call on Tuesday that the United States would provide Ukraine with $625 million in new security assistance, including High Mobility Artillery Rocket System launchers.