Mr Putin said he would "calmly develop" the annexed territories. [Photo Credit: BBC News]

Russia’s President Vladimir Putin has signed the final papers to annex four regions of Ukraine – even as his military suffered further setbacks.

The Luhansk, Donetsk, Zaporizhzhia and Kherson regions are “accepted into the Russian Federation” the documents say.

But in two of those areas – Luhansk and Kherson – Ukraine said it has been retaking more villages.

Mr Putin also signed a decree to formalise Russia’s seizure of the nuclear power plant in Zaporizhzhia.

Last Friday, the Russian leader held a grand ceremony in the Kremlin, where he signed agreements with the Moscow-installed leaders of the four regions.

The move followed self-proclaimed referendums in the areas, denounced as a “sham” by the West.

But on the ground, there appears to be a different reality, with Ukrainian forces making gains in both the south and the east.

Serhiy Haidai, Ukrainian governor of Luhansk, told the BBC on Wednesday that six villages in the region had been recaptured.

And President Zelensky later said Ukraine had liberated three more villages in the southern region of Kherson.

That followed a series of gains in Kherson the previous day, including the strategically key village of Davydiv Brid.

Meanwhile, Ukraine says multiple explosions were heard in the southern city of Zaporizhzhia before dawn on Thursday.

The governor of the region said rockets were aimed at residential buildings and there had been significant destruction. Rescuers were already pulling bodies from the rubble, he added.

Kremlin spokesman Dmitry Peskov said Russia would retake any territory that had been lost to Ukrainian forces.

Facing questions over the recent losses, he told reporters: “There is no contradiction here. They will be with Russia forever, they will be returned.”