NATO Secretary General Jens Stoltenberg said that it’s impossible to know when the war in Ukraine will end – but that the world should be prepared for fighting that continues for years. Stoltenberg’s forecast, in an interview published Saturday in Germany’s Bild newspaper, comes as the United States and its allies are preparing for a drawn-out conflict. After a visit to Kyiv, British Prime Minister Boris Johnson said it is critical to maintain visible support for Ukraine, even as “Ukraine fatigue is setting in.”

Russian morale “highly likely remains especially troubled,” Britain’s Defense Ministry said Sunday. Russian commanders in eastern Ukraine continue to face dissent from troops, with whole units refusing orders in some cases and armed standoffs happening between officers and soldiers. Ukrainian forces have probably suffered desertions in recent weeks, according to the assessment.

A former U.S. soldier who disappeared in Ukraine is alive, according to his family members, who said they have seen a video of him from after he was reportedly captured by Russian forces.

Russian forces control most of Severodonetsk, a bitterly contested city crucial to Russian hopes of advancing in the eastern Luhansk region, governor Serhiy Haidai said Sunday morning. He added that Russia has massed reserves in the area in preparation for a large attack.

“Russia is trying to make Kharkiv a front-line city,” Vadym Denysenko, an adviser to Ukraine’s Interior Ministry, said Sunday.

Kharkiv was an early target in the Russian invasion of Ukraine, when shelling forced the population to take shelter in basements and metro stations. More recently, it has been spared the fierce fighting that has raged farther south in the Luhansk region. On Saturday, however, Russian forces stepped up offensive operations to prevent Ukrainian troops from advancing toward the border, which lies about 25 miles north of the city.

The General Staff of the Ukrainian Armed Forces said Moscow wants to prevent engagement with Russian troops trying to supply their forces farther south in Slovyansk, according to the Washington-based Institute for the Study of War. Ukraine also said Russian troops are laying additional rail tracks to restore supply lines to Slovyansk.

An oil refinery near Izyum was hit by Russian missiles on Saturday, causing a fire that was still burning Sunday, regional governor Oleh Synyehubov said. Russian shelling in areas south of Kharkiv city killed a 73-year-old man and injured five other people, he said.

Over the border in the Belgorod region, Russia has massed between five and seven battalion tactical groups, as well as attack aircraft and helicopters, according to Oleksiy Arestovych, an adviser to Ukrainian President Volodymyr Zelensky. He said these forces are intended for an attack on Kharkiv. A Russian battalion tactical group normally consists of 600 to 800 officers and troops, although analysts have noted that some Russian army BTGs are understrength and made up of inexperienced personnel.

Two Ukrainian commanders who aided in the months-long defense of the Azovstal steel plant in the battered port city of Mariupol have been transferred to Russia “for investigation,” the Russian state news agency Tass reported.

The fates of hundreds of fighters who surrendered to Russian forces last month remain unclear. They were taken out of the plant on buses under Russian guard to unknown destinations.

Sviatoslav “Kalina” Palamar, deputy commander of the Azov Regiment, and Serhiy Volynsky, a commander of Ukraine’s 36th Marine Brigade, have been taken to Russia from the Donetsk region, according to unnamed Russian law enforcement sources. They are among a group of officers “from various Ukrainian units” who were transferred there.

The report did not say where in Russia they were sent. The Washington Post could not independently verify the report, and there has been no comment on it from Ukrainian officials. Russian separatists control parts of Donetsk as a self-declared breakaway region, recognized only by Russia as an independent entity.

Palamar was one of the public faces of Ukrainian resistance at Azovstal, as hundreds of fighters operating in underground tunnels battled Russian attempts to capture the plant. Civilians sheltering in the complex were gradually evacuated, and Russian forces claimed full control of Azovstal on May 20 after a negotiated surrender.

Zelensky said early Sunday that he had returned to Kyiv after visiting the front lines in southern Ukraine and that “we will not give away the south to anyone.”

In the cities of Mykolaiv and Odessa, which were ravaged by heavy Russian assaults, “the losses are significant,” Zelensky said in a video message.

“Many houses were destroyed. Civilian logistics were disrupted. There are many social issues,” he said.

As the war drags on, Ukrainian fighters are still holding strong, he said. “Their mood is confident, and looking into their eyes it is obvious that they all do not doubt our victory,” he said.

German Chancellor Olaf Scholz said the Group of Seven major industrial countries will make clear at an upcoming gathering that they intend to back Ukraine in its fight against the Russian invasion for “as long as necessary.”

In an interview Saturday with the German news agency Deutsche Presse-Agentur, Scholz said Russian President Vladimir Putin “obviously hopes that everything will fall into place once he has conquered enough land and the international community will return to business as usual. That is an illusion.”

Scholz made similar remarks about Germany’s long-term commitment to Ukraine’s war effort during a visit to Kyiv late last week with French President Emmanuel Macron and Italian Prime Minister Mario Draghi.

The leaders of the European Union’s three largest economies announced during the Thursday visit that they were backing Ukraine’s candidacy to join the 27-member bloc, a move that Zelensky has fiercely advocated as his country loses ground in the face of Russia’s invasion.

G-7 leaders are meeting in the Bavarian Alps next week, with Ukraine set to top the agenda.

Actor Ben Stiller met with Ukrainian refugees in Poland as part of a visit with the Office of the U.N. High Commissioner for Refugees.

He said in a statement posted Saturday on Instagram that he was there to “learn, to share stories that illustrate the human impact of war and to amplify calls for solidarity.”

Stiller, a goodwill ambassador for the U.N. refugee agency, is not the first celebrity to meet with Ukrainian refugees in the region. Angelina Jolie, a U.N. special envoy for refugees, met with impacted families in April in Lviv, Ukraine.

Ukraine’s parliament has passed measures restricting the availability of Russian music and books in the country.

The Verkhovna Rada banned Russian music from being performed in public and broadcast on radio or TV stations, and it prohibited tours by Russian performers – unless the performer supports Ukraine.

In a separate measure, lawmakers moved to ban the import of Russian books.

“The Russian ‘cultural’ ship is following the military one!” Oleksandr Kornienko, the first deputy chairman of the Verkhovna Rada, said in a Telegram post cheering the decision. He added, “We want to read and listen to Ukrainian!”

Authorities announced the passage of the bills on Sunday.