According to Ukrainian authorities, Russian artillery pounded Ukrainian defense positions in the country’s east as Moscow stepped up its efforts to seize more territory there, while Kyiv sought to win international support for its peace terms.

Volodymyr Zelensky, the president of Ukraine, claimed that more than 400 artillery attacks against Ukrainian positions had been made by Russian forces on Sunday alone. In a video address late on Sunday, Mr. Zelensky said, “Thank you to every man and woman who is holding their positions and aiding our defense forces.”

The weather, according to Mr. Zelensky, was slowing Russia’s advance in the eastern Ukrainian regions of Donetsk and Luhansk, but fierce fighting was still going on.

Serhiy Haidai, the exiled governor of the Luhansk region, claimed that Ukraine was regaining territory there “step by step,” but he did not specify which areas had been reclaimed.

The construction of defensive lines in the east was given top priority by Russia as its forces dug in ahead of winter, according to the U.K.’s Defense Ministry on Monday. The war’s front lines are expected to move slowly in the coming weeks as temperatures drop, according to many observers.

As the nine-month mark for Russia’s full-scale invasion of Ukraine approaches, Kyiv is under pressure from some of its Western backers to show that it is prepared for talks with Moscow due to worries about the war’s potential effects on the world economy. The Ukrainian government is pushing to determine the discussion’s agenda.

On November 8, Mr. Zelensky stated that he was open to “genuine peace talks” with Moscow and listed Ukraine’s demands as the complete restoration of Ukrainian control over its territory, payment of damages for Moscow’s invasion, and the prosecution of war criminals.

Zelensky stated: “We will do everything so that the world accepts the Ukrainian peace formula” in his evening address on Sunday.

But given the hardening of both sides’ positions and the conviction in both capitals that they can prevail on the battlefield, the prospects for talks between Kyiv and Moscow, which sputtered to a halt in the spring, remain slim.

Konstantin Kosachev, the deputy speaker of Russia’s upper house of parliament, stated in an interview with Russian media on Monday that a “normalization” of relations between the two nations would only be possible after a change of government in Ukraine. Mr. Kosachev told the newspaper Argumenty I Fakty, “I don’t expect anything positive from the current leadership in Ukraine.

According to Dmitry Peskov, a spokesman for the Kremlin, Russia’s objective in Ukraine is not regime change.

The International Atomic Energy Agency issued a warning, stating that further shelling of the nuclear power plant in Zaporizhzhia, Ukraine, could result in a catastrophe.

On Sunday, Russia and Ukraine exchanged accusations over who had shelled the Russian-controlled plant, which had been producing 20% of Ukraine’s electricity prior to the war. Russia claimed that more than a dozen striking areas of the facility, including the power line feeding the power plant, had been hit by large-caliber artillery shells.

Without assigning blame, the IAEA stated that shelling had damaged structures, systems, and equipment, with some explosions taking place close to the reactors. According to the agency, the site’s radiation levels remained normal, and no casualties were reported. It also stated that the plant’s external power sources were unaffected.

Russia’s Belgorod region, which is close to the Ukrainian border, is governed by Vyacheslav Gladkov, who declared on Monday that authorities were extending a period of increased alertness for what he called the threat of terrorist attacks through December 6. Russian authorities claim that there have been several strikes in Belgorod recently, some of which they have attributed to Ukraine. Since early April, several other Russian regions close to the Ukrainian border have been on high alert, allowing for increased security patrols and checkpoints across the entire region.

Despite Ukrainian victories in forcing Russian forces out of some occupied territories, citizens of many Ukrainian cities are bracing themselves for a difficult winter with frequent outages of electricity, heating, and water supplies amid a concerted Russian campaign to harm vital infrastructure throughout the country.

Mr. Zelensky said on Sunday that engineers were working around the clock to repair Ukraine’s electricity grid after the latest Russian attacks, and that there were planned power outages in 15 regions as part of efforts to ease pressure on the grid.