President Vladimir Putin completed the formal annexation of more than 15% of Ukraine on Wednesday just as Russian forces battled to halt Ukrainian counter-offensives across swathes of the territory.

Russia's president Vladimir Putin

In the biggest expansion of Russian territory in at least half a century, Putin signed laws admitting the Donetsk People's Republic (DPR), the Luhansk People's Republic (LNR), Kherson region and Zaporizhzhia region into Russia.

"President Vladimir Putin has signed four federal constitutional laws on the entry of the Donetsk and Luhansk People's Republics, Zaporizhzhia and Kherson regions into the Russian Federation," the lower house of parliament said.

"He also signed the relevant laws on ratification," the Duma said.

Russia declared the annexations after holding what it called referendums in occupied areas of Ukraine. Western governments and Kyiv said the votes breached international law and were coercive and non-representative.

The areas that are being annexed are not all under control of Russian forces which are battling Ukrainian forces.

More than seven months into a war that has killed tens of thousands and triggered the biggest confrontation with the West since the 1962 Cuban Missile crisis, Russia's most basic aims are still not achieved.

In recent days, Russian forces have withdrawn from areas of eastern and southern Ukraine where they have been under severe pressure from a Ukrainian counteroffensive which has prompted criticism from senior Putin allies of the war machine.

Together with Crimea, which Russia annexed in 2014, Putin's total claim amounts to more than 22% of Ukrainian territory, though the exact borders of the four regions he is annexing are still yet to be finally clarified.

Russia, which recognised Ukraine's post-Soviet borders in the 1994 Budapest Memorandum, will never give the regions back, Putin said on Friday at a grand Kremlin treaty-signing ceremony which brought the partially controlled regions into Russia.

Russia's parliament said people living in the annexed regions would be granted Russian passports, the Russian Central Bank would oversee financial stability and the Russian rouble would be the official currency.

In justifying the Feb. 24 invasion, Putin said that Russian speakers in Ukraine had been persecuted by Ukraine which, he said, the West was trying to use to undermine Russian security.

Ukraine and its Western backers say that Putin has no justification for what they say is an imperial-style land grab. Kyiv denies Russian speakers were persecuted.

Now Putin casts the war as a battle for Russia's survival against the United States and its allies, which he says want to destroy Russia and grab its vast natural resources.