KYIV, Ukraine — Russian President Vladimir Putin has signed laws formally absorbing four Ukrainian regions into Russia, even as its military is struggling to hang on to control of the regions it illegally annexed.

The documents finalizing the annexation carried out in defiance of international laws were published on a Russian government website on Wednesday morning.

Earlier this week, both houses of the Russian parliament ratified treaties making the Donetsk, Luhansk, Kherson and Zaporizhzhia regions part of Russia. That followed Kremlin-orchestrated “referendums” in the four regions that Ukraine and the West have rejected as a sham.

On the ground, Moscow’s war in Ukraine has entered a new, more dangerous phase. Russia faces mounting setbacks, with Ukrainian forces retaking more and more land in the east and in the south — the very regions Moscow has pushed to annex.

The borders of the territories Russia is claiming still remain unclear, but the Kremlin has vowed to defend Russia’s territory — the newly absorbed regions, too — with any means at its disposal, including nuclear weapons.

Ukrainian President Volodymyr Zelenskyy responded to the annexation by announcing a fast-track application to join NATO and formally ruling out talks with Russia. Zelenskyy’s decree, released Tuesday, declares that holding negotiations with Putin has become impossible after his decision to take over the four regions of Ukraine.

The head of Zelenskyy’s office, Andriy Yermak, wrote on his Telegram channel shortly after Putin signed the annexation that “the worthless decisions of the terrorist country (Russia) are not worth the paper they are signed on.

“A collective insane asylum can continue to live in a fictional world,” he added.

Kyiv’s military said Wednesday they have recaptured more villages in the southern Kherson region as a part of their massive counteroffensive effort. Operational Command South said that the Ukrainian flag has been raised above Liubymivka, Khreschenivka, Zolota Balka, Biliaivka, Ukrainka, Velyka and Mala Oleksandrivka villages.

On the battlefield on Wednesday morning, multiple explosions rocked Bila Tserkva, setting off fires at what were described as infrastructure facilities in the city to the south of the capital Kyiv, regional leader Oleksiy Kuleba said on Telegram.

Early indications are that the city was attacked by so-called “kamikaze” or suicide drones, he said.

Bila Tserkva is about 80 kilometers (50 miles) south of Kyiv.

Russia has increasingly been using suicide drones in recent weeks, posing a new challenge to Ukrainian defenses. The unmanned vehicles can stay aloft for long periods of time before diving into their targets and detonating their payload at the last moment.

Many of the earlier attacks by the Iranian-made drones happened in the south of the country and not near the capital, which hasn’t been targeted for weeks.

In a later post, Kuleba said that a total of six Shahed-136 drones struck the city, one of the largest in the region after Kyiv itself. One person was injured in the attacks.

Dozens of rescue workers were on the scene and still working to extinguish the fires hours after the attacks were reported, he said.