Russian President Vladimir Putin officially announced the annexation of four Ukrainian territories on Wednesday, even as a major battlefield reversal recently has reduced the number of occupied territories that Moscow controls.

Russia has escalated its seven-month war, warning of annexation, mobilisation of troops and possible resort to nuclear weapons to protect all its territories. Putin has now signed a law formally incorporating four regions representing about 18% of Ukraine’s territory into Russia; the state-owned TASS news agency reported Wednesday morning.

The Russian leader’s signature is the final stage of the legislative process. Both houses of the Russian parliament have approved the plan. Kyiv and its Western allies have said Russia’s annexation attempt is an illegal land grab. Ukraine has said its forces will retake any territory occupied by Russian forces, which will never be recognised.

Ukrainian President Volodymyr Zelensky said late Tuesday that his forces had made significant and rapid progress against Russian forces over the past week, retaking dozens of towns in the southern and eastern regions that Russia had declared annexation. “This week alone, dozens of population centres have been liberated since Russia’s pseudo-referendum. These are concentrated in the Kherson, Kharkiv, Luhansk and Donetsk regions,” Zelensky said Key said.

Zelensky named eight towns in southern Kherson that were recently recaptured. Russia does not fully control any of the four areas it claims — Donetsk and Luhansk in eastern Ukraine and Zaporizhzhia and Kherson in the south — and the Kremlin says it has not yet identified the annexed territories. Russian troops in the Donetsk and Kherson regions, which have been forced to retreat recently, are already digging new positions they hope will stop Ukraine’s advance.

Moscow began annexing the regions following a so-called referendum on September 23, which Kyiv and Western governments denounced as illegal and coercive. A Tuesday video released by the Ukrainian Defence Ministry showed the Ukrainian flag being raised over Davydiv Brid, a neighbourhood in Kherson.

A map released by the Russian Defence Ministry on Tuesday also appeared to show the rapid withdrawal of Russian troops from eastern and southern Ukraine, which have been under heavy pressure from a Ukrainian counteroffensive.

In the east, Ukrainian forces have been expanding their offensive after capturing the main Russian fort in the northern Donetsk town of Lehman.

“In some areas of the front line, we can expand the area under our control from 10 kilometres to 20 kilometres,” the Ukrainian Armed Forces Southern Combat Command said on Wednesday.

The UAF said in its daily report that Russian troops were destroying their ammunition stocks and trying to destroy bridges and border crossings to slow Ukraine’s advance. In Kherson, it said that withdrawing Russian troops was laying mines in “infrastructure” and houses.

According to the report, in the past 24 hours, Russia lost 31 soldiers and more than 40 pieces of equipment, including eight tanks, 26 armoured vehicles and a large-calibre howitzer. Moscow hopes the “partial mobilisation” announced two weeks ago will help reverse a series of battlefield setbacks, with some officials saying they intend to retake territory ceded to Ukraine.

Russia has so far recruited more than 200,000 reservists out of a planned 300,000 reservists; RIA Novosti quoted Defence Minister Shoigu saying on Tuesday. However, many Russian men have fled the country instead of fighting in Ukraine, and Russian lawyers say they are doing their best to advise men who want to avoid being called up.

US President Joe Biden told Zelensky in a phone call on Tuesday that the US would provide Ukraine with $625 million in new security aid, including High Mobility Rocket Artillery System (HIMARS) launchers, to boost Ukraine.