President Volodymyr Zelensky has said that Ukrainian counter-offensive operations are under way, but declined to divulge details, telling a press conference to pass on to Vladimir Putin that Ukraine's generals are optimistic.
The Ukrainian leader shrugged at a press conference in Kyiv when asked about comments by the Russian president, who said that Kyiv had begun its counter-offensive, but failed to make progress.
"Counter-offensive and defensive actions are taking place in Ukraine, but I will not say in detail what stage they are at," Mr Zelensky said, listing Ukraine's top military brass by name.
"They (the generals) are all in a positive mood. Pass that on to Putin," he said with a smile standing alongside visiting Canadian Prime Minister Justin Trudeau.
Ukraine has said for months it plans to conduct a major counter-offensive to recapture tracts of land occupied by Russiain the south and east.
But it is enforcing strict operational silence and has denied it has begun the main operation for now.
Russia says Ukraine launched a big offensive push this week, but that Kyiv's forces failed to breach its defences and also sustained heavy casualties.
With scant independent reporting from the front lines, it has been difficult to assess the state of the fighting.
Britain's Ministry of Defence said Ukraine had conducted "significant" operations in several eastern and southern partsin the last 48 hours, with Russian defences breached in places.
"In some areas, Ukrainian forces have likely made good progress and penetrated the first line of Russian defences. In others, Ukrainian progress has been slower," it said, also characterising the Russian military's performance as mixed.
"Some (Russian) units are likely conducting credible manoeuvre defence operations while others have pulled back in some disorder, amid increased reports of Russian casualties as they withdraw through their own minefields."
'We are counter-attacking'
Ukraine's counter-offensive is expected to use thousands o ftroops that have been trained and equipped by the West, but Russia has built huge fortifications in occupied territory to prepare, while Kyiv also lacks air supremacy.
The south is seen as a key strategic priority for a Ukrainian push that could aim to recapture Europe's biggest nuclear plant and cut the Russian land bridge to the occupied Black Sea peninsula of Crimea, dividing Russian forces.
Ukraine reported gains in the east this week around Bakhmut, the devastated city that Russia said it captured last month in the bloodiest fighting of the war.
Ukrainian military spokesman Serhiy Cherevaty today said Kyiv had made new gains.
"We're trying...to conduct strikes on the enemy, we are counter-attacking. We've managed to advance up to 1,400 metres on various sections of the front," Mr Cherevaty said.
Russia's Defence Ministry said that Ukrainian forces had continued in the past 24 hours "unsuccessful" attempts to attack in southern Donetsk and Zaporizhzhia regions, as well as in the area of the eastern city of Bakhmut.
Ukraine's third assault brigade published footage of what it said were offensive operations near Bakhmut where it said had inflicted Russian casualties and hit an ammunition dump.
Reuters was unable to independently verify the battlefield situation and statements by both sides.