KHARKIV, UKRAINE (REUTERS) - Ukraine said on Tuesday (May 10) its forces had recaptured villages from Russian troops north and north-east of Kharkiv, pressing a counter-offensive that could signal a shift in the war's momentum and jeopardise Russia's main advance.

Ukrainian troops in recent days recaptured the settlements of Cherkaski Tyshky, Ruski Tyshki, Borshchova and Slobozhanske, north of Ukraine's second-largest city, said Tetiana Apatchenko, a press officer with the main Ukrainian force in the area.

Defence Ministry adviser Yuriy Saks said the Ukrainian successes were pushing Russian forces out of range of Kharkiv, located in the northeast, which has been under perpetual bombardment since the war began.

"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."

In Washington, top US intelligence officials said the war was at a stalemate. President Vladimir Putin appeared to be preparing for a long conflict, and a Russian victory in the Ukraine's eastern Donbas region might not end the war, director of national intelligence Avril Haines said.

But the counterattack near Kharkiv could signal a new phase, with Ukraine now going on the offensive after weeks in which Russia mounted a massive assault without making a breakthrough.

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

"Ukrainians are getting close to the Russian border. So all the gains that the Russians made in the early days in the north-east of Ukraine are increasingly slipping away," said Neil Melvin of the RUSI think-tank in London.

Challenges

During a Red Square military parade on Monday marking the end of World War II, Putin exhorted Russians to keep fighting but gave no indication of his further strategy.

Since Russia was forced to abandon an assault on the capital Kyiv at the end of March, its main force has been trying to encircle Ukrainian troops in the Donbas, using the city of Izyum south of Kharkiv as a base. Ukrainian troops have so far mostly held out against assaults from three directions.

But by pushing back near Kharkiv, Ukraine could now force Moscow to switch to trying to defend its own long supply lines to Izyum. Western military analysts said there were signs the counter-attack was already sapping Russia's advance.

"Our assessment is that they're (Russians) having to pull some forces away from the axes leading to the control of the Donbas region because of what has happened in Kharkiv, and it just underscores the challenges they have," said retired US General Jack Keane, now chairman of the Institute for the Study of War think-tank.

In the south, Russian forces were again pummelling the Azovstal steelworks in Mariupol, 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.

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 in a social media post 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 and rockets. Reuters was unable to verify the situation.

In Odesa, firefighters battled blazes until the early hours of Tuesday after seven Russian missiles hit a shopping centre and depot on Monday. One person was killed and five people were injured, Ukraine's armed forces said. The missile strikes interrupted talks between European Council President Charles Michel and Ukrainian Prime Minister Denys Shmyhal.

Ukraine said its armed forces in the Donbas on Tuesday destroyed 12 Russian tanks and 19 armoured vehicles and shot down three aircraft. Pavlo Kyrylenko, regional governor for the Donbas' Donetsk region, said three residents were killed and three others injured on Tuesday.

'Bit of a stalemate'

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

​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 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."

Western countries have placed sweeping sanctions on Moscow and are taking steps to ban or phase out the use of Russian energy.

Ukraine, which has remained a major route for Russian gas to Europe even after the invasion, said on Tuesday it would suspend use of a transit point for some Russian gas headed to Europe, blaming Moscow for the move. It will redirect the gas from that transit point, which is in an area occupied by Russian forces, to another in a Ukraine-controlled area.

The United States and Europe have promised to keep supplying Kyiv with arms and humanitarian aid. US lawmakers were expected to vote Tuesday on a US$40 billion Ukraine aid proposal, including a massive new weapons package.