Ukraine said on Tuesday its forces had recaptured villages from Russian troops, pressing a major counter-offensive in the northeast of the country that could signal a shift in the war’s momentum and jeopardise “The Ukrainian army was able to push these war criminals to a line beyond the reach of their artillery.”’s main advance.

Tetiana Apatchenko, press officer for the 92nd Separate Mechanized Brigade, the main Ukrainian force near Kharkiv, confirmed that Ukrainian troops had recaptured the settlements of Cherkaski Tyshky, Ruski Tyshki, Borshchova and Slobozhanske, in a pocket north of Kharkiv in recent days.

Yuriy Saks, an adviser to Defense Minister Oleksiy Reznikov, said the successes were pushing Russian artillery out of range of parts of Kharkiv, Ukraine’s second largest city, which has been under bombardment since the war’s earliest days.

“The military operations of the Ukrainian armed forces around Kharkiv, especially north and northeast of Kharkiv, are sort of a success story,” Saks told Reuters.

“The Ukrainian army was able to push these war criminals to a line beyond the reach of their artillery.”

The counterattack could signal a new phase in the war, with Ukraine now going on the offensive after weeks in which Russia mounted a massive assault that Ukrainian troops mostly held off.

By pushing back Russian forces who had occupied the outskirts of Kharkiv since the early days of the war, the Ukrainians are moving into striking distance of the rear supply lines sustaining the main Russian attack force further south.

“They’re trying to cut in and behind the Russians to cut off the supply lines, because that’s really one of their (the Russians’) main weaknesses,” said Neil Melvin of the RUSI think-tank in London.

“Ukrainians are getting close to the Russian border. So all the gains that the Russians made in the early days in the northeast of Ukraine are increasingly slipping away.”

The setbacks near Kharkiv deal a blow to Moscow’s war plans at precisely the moment when Western capitals believed President Vladimir Putin had been hoping to present a major victory for a holiday marking the end of World War Two.

On Monday, Putin presided over a huge Red Square military parade for the Victory Day holiday. Western countries had worried that, in the absence of major battlefield success to announce, he might instead order a nationwide mobilisation. But in the event, he did neither – exhorting Russians to keep fighting but giving no indications about his further strategy.

Since Russia was forced to abandon its assault on the capital Kyiv at the end of March, its main attack force has been trying to encircle Ukrainian troops in the eastern region known as the Donbas. The Ukrainian forces have been holding out against intensive assaults from three directions.

By pushing in north of Kharkiv, Ukraine could now try to turn the tables, and force Moscow to switch to trying to defend its own long supply lines, which stretch from the Russian border to the city of Izyum south of Kharkiv.

In the south, Russian forces were again pummelling the Azovstal steelworks in Mariupol on Tuesday, trying to capture the last bastion of Ukrainian resistance in the ruined city where Ukraine says tens of thousands of people have died under two months of Russian siege and bombardment.

Scores of civilians have been evacuated from the steelworks in recent days, but an aide to Mariupol’s mayor, Petro Andryushchenko, said at least 100 still remained inside.

Ukraine’s Azov Regiment, holding out in Azovstal, said on the Telegram messaging app that in the past 24 hours, 34 Russian aircraft had flown over the plant including 8 sorties by strategic bombers. It said the plant had come under fire from the Russian navy and from tanks, artillery fire and rockets.

Reuters was unable to verify the situation at the plant. Russia did not immediately comment on his remarks and has denied targeting civilians.

Germany’s Foreign Minister Annalena Baerbock visited Ukraine on Tuesday and toured Bucha, the suburb north of Kyiv where Russian forces left behind hundreds of corpses of killed civilians when they withdrew at the start of April. She said the killers must be punished.

“That is what we owe to the victims,” she said. “And these victims, you can feel that here very intensely, these victims could have been us.”

Baerbock was the first German cabinet minister to visit Ukraine since the start of the war, days or weeks after visits by senior officials from other Western countries. A visit from Germany had been controversial because Kyiv had openly rebuked the government in Berlin for being slow to disavow years of close economic ties with Russia.

In addition to the heavy battles near the front, Russia is still using missiles to strike targets deep inside Ukraine.

Firefighters battled blazes in Odesa until early hours on Tuesday after Russian missiles struck the Black Sea port. One person was killed and five people were injured when seven missiles hit a shopping centre and a depot, Ukraine’s armed forces said on Facebook.

Rescue workers combed through piles of rubble. Ukrainian emergency services said all the fires set off by the strikes were extinguished early on Tuesday.

European Council President Charles Michel visited Odesa on Monday, and his meeting with Ukrainian Prime Minister Denys Shmyhal was interrupted by the missile attack. Their talks continued in a bomb shelter, according to Shmyhal’s official Twitter account.

The number of Ukrainians who have fled their country since Russia’s invasion on Feb. 24 was approaching 6 million, according to the United Nations, which says the refugee crisis is the fastest growing since World War Two.

U.S. President Joe Biden said on Monday he was worried Putin “doesn’t have a way out right now, and I’m trying to figure out what we do about that”.