Eleven months since Russia invaded its southern neighbour, the fighting is centred on the town of Bakhmut in Ukraine's east, where Russia's Wagner mercenaries and Ukrainian forces have been locked in a battle of attrition.
Russia's defence ministry said for the second straight day on Sunday its forces were improving their positions in Ukraine's southern region of Zaporizhzhia, although a Ukrainian military representative told the state broadcaster the situation there was "difficult" but stable.
Reuters was not able to independently verify battlefield accounts.
Ukrainian officials have been calling on Western allies to supply them with the modern German-made tanks for months but Berlin has held back from sending them or allowing other NATO countries to do so.
Leopard tanks, which are held by an array of NATO countries but whose transfer to Ukraine requires Berlin's approval, are seen by defence experts as the most suitable for Ukraine.
Western allies pledged billions of dollars in weapons for Ukraine last week but failed to persuade Germany to lift its veto on providing the tanks.
But in an apparent shift in Germany's position, foreign minister Annalena Baerbock said her government would not block Poland if it were to send its Leopard 2 tanks without German approval.
"The question has not been asked but if we were asked we would not stand in the way," she told France's LCI TV asked about her government's reaction to any such Polish decision.
Germany has been under heavy pressure to let Leopards go to Ukraine but Chancellor Olaf Scholz's Social Democrat party is traditionally sceptical of military involvements and wary of sudden moves that could trigger Russia.
Baerbock's remarks appeared to go further than Scholz's comments at a summit in Paris earlier on Sunday that all decisions on weapons deliveries would be made in co-ordination with allies, including the United States.
Ukraine says the heavily armoured battle tanks would give its ground troops more mobility and protection ahead of a new Russian offensive expected in the coming months.
But Germany has appeared to have tied any such contribution to a US move to send its Abrams tanks, something American officials have said they are reluctant to do because the vehicles are complicated to maintain.
American lawmakers pushed their government on Sunday to export M1 Abrams main battle tanks to Ukraine, saying sending a symbolic number would be enough to push European allies to do the same.
Britain recently said it was supplying 14 Challenger 2 tanks to Ukraine.
Its foreign minister, James Cleverly, said on Sunday it still wanted an international deal to provide Ukraine with the German-made tanks.
French President Emmanuel Macron, meanwhile, said he did not rule out the possibility of sending Ukraine Leclerc tanks.
Last week, the Kremlin's spokesman said Western countries supplying additional tanks to Ukraine would not change the course of the conflict but would add to the problems of the Ukrainian people.
A close ally of President Vladimir Putin said on Sunday deliveries of offensive weapons to Kyiv that threaten Russia's territories would lead to a global catastrophe and make arguments against using weapons of mass destruction untenable.
Vyacheslav Volodin, the speaker of Russia's lower house of parliament, warned US and NATO support for Ukraine was leading the world to a "terrible war".
