Officials in Russian-occupied Ukraine announced plans for Russia to annex four regions in the country’s east and south, while Moscow moved to clear the way for a broader mobilization and threatened NATO attacks in response to Ukraine’s rapid advance.

Russian-controlled areas of Ukraine’s Donetsk, Luhansk, Kherson, and Zaporizhzhia regions said they will hold three-day referendums on joining Russia beginning this Friday, the latest effort by Moscow to consolidate its hold on territory it took months to capture but now risks losing to Ukrainian forces.

The country’s lower house of parliament also approved legislation that could help address the country’s troop shortage on the battlefield, raising fears that a full-scale mobilization could be announced within days.

Ukraine’s leadership has reiterated a pledge to liberate all occupied territories and capitalize on the momentum gained since its lightning offensive through Russian-held territory in the northeast earlier this month.

Ukrainian President Volodymyr Zelensky said in his daily video address on Monday evening that the country’s armed forces were working to stabilize their hold in the liberated Kharkiv region, causing Russian forces to panic.

Denis Pushilin, the Russian-installed leader of the occupied Donetsk region in east Ukraine, said on Russian state television on Tuesday that he was working hard to hold a vote. According to comments carried by Russian state news agency RIA Novosti, authorities in Kherson, a region under partial Russian control in southern Ukraine, have also reiterated their desire for an immediate referendum.

For years, Russia has issued passports to residents of the self-proclaimed Luhansk and Donetsk People’s Republics, proxy states carved out of eastern Ukraine during a Russian-backed armed conflict that began in 2014. Moscow has spent a lot of money to keep its grip on the country.

However, the Ukrainian military offensive in the south, north, and east, which has liberated the northeastern Kharkiv region and reclaimed more than 3,000 square miles of territory, is causing Russian collaborators in occupied areas to rethink their plans and admit that the security situation is unstable.

Russian-allied officials in the southern Kherson and Zaporizhzhia regions initially indicated that referendums would be held on September 11, but when Ukraine swept through the northeastern Kharkiv region and captured villages en route to Kherson earlier this month, they said the votes would be postponed.

Hawkish members of Russia’s political establishment have backed the initiative, arguing that incorporating occupied parts of Ukraine into Russia proper would embolden Russia and give legitimacy to what it could portray as retaliatory strikes against its territory by NATO-backed forces.

Russian officials, enraged by Russia’s humiliation, are amplifying the calls and endorsing moves that could escalate the conflict. Dmitry Medvedev, deputy chairman of the Russian Security Council, wrote on Telegram Tuesday that by amending the constitution, the incorporation of new territories into Russia would become irreversible even under future presidents.

Russia’s parliament advanced legislation on Tuesday that tightens penalties for evading mobilization, desertion, surrender, and looting during wartime, appearing to ease the legal path to mobilization. The State Duma, Russia’s lower house, approved amendments to the criminal code that included the concepts of mobilization and martial law. However, the proposed legislation must still pass through the Federation Council, Russia’s upper house of parliament, and be signed by Russian President Vladimir Putin.

The debate over annexing parts of Ukraine comes as Kyiv’s advance slows but continues to push Russia out of strategic areas such as a swath of land east of the Oskil River in the Kharkiv region, and as Russia scrambles for additional manpower to continue its war.

Russia has referred to its invasion of Ukraine as a special military operation from the start, but declaring it a war, as Ms. Simonyan suggested, would broaden the Kremlin’s political options, including the ability to frame attacks on Russian-held territory as attacks on Russia itself, analysts say.