KYIV -President Volodymyr Zelenskiy said on Saturday that Ukrainian counter-offensive operations were under way, but declined to divulge details, telling reporters to pass on to Russian President Vladimir Putin that Ukraine's generals are optimistic.

The Ukrainian leader, in his trademark khaki fatigues, shrugged at a press conference in Kyiv when asked about comments by Putin, who said on Friday 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," Zelenskiy 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.

In his nightly video address, Zelenskiy provided few details while urging troops to keep fighting.

"Thank you to all those who holds their positions and those who advance," he said, citing the eastern and southern fronts, where fighting is heaviest.

Ukraine's general staff said its forces had repelled enemy attacks around Bakhmut and Maryinka, sites of heavy clashes in the east. Russian forces, it said, "continue to suffer heavy losses which they are trying to conceal".

Deputy Defence Minister Hanna Maliar made it plain on Telegram that the military would issue no statements until battlefield positions became clear.

"Ask yourself this...am I prepared to receive information about the liberation of this or that town not when our troops enter it, but once they establish a stronghold?" she wrote.

Ukraine has said for months it plans to conduct a major counter-offensive to recapture land occupied by Russia in the south and east. But it is enforcing strict operational silence for now and has denied it has begun the main operation.

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 parts in the last 48 hours, with Russian defences breached in places.

SOME PROGRESS: BRITISH MINISTRY

"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."

Ukraine's counter-offensive is expected to use thousands of troops 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 this week around Bakhmut, the city that Russia said it captured last month and on Saturday, military spokesman Serhiy Cherevaty reported 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 (0.87 mile) on various sections of the front," Cherevaty said.

Russia's Defence Ministry said Ukrainian forces had in the past 24 hours made "unsuccessful" attempts to attack in southern Donetsk and Zaporizhzhia regions, as well as near 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.

  - Reuters