Ukraine 'pushing Russian troops back'

Ukrainian Su-25 jet
Ukrainian Su-25 jets have taken part in an attack on Russian positions in the Donetsk region. -AP

Ukraine says its forces have 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 Russia's main advance.

Tetiana Apatchenko, press officer for the 92nd Separate Mechanised 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 Defence 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," Neil Melvin of the RUSI think-tank in London said.

"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."

By pushing in north of Kharkiv, Ukraine could now try to turn the tables, and force Russia 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 able to leave 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 - a militia set up by Ukrainian ultra-nationalists in 2014 and later incorporated as a regiment in Ukraine's national guard - in Azovstal said on the Telegram messaging app that in the past 24 hours, 34 Russian aircraft had flown over the plant including eight 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."

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

US 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".