The much-vaunted counteroffensive, which is nearing the three-month mark, has retaken more than a dozen villages but no major settlements with soldiers hampered by vast Russian minefields and defensive lines.

This week, unnamed U.S. officials vented frustration at the slow progress of the operation and even faulted Ukrainian strategy, according to Western reports that drew Kyiv's ire.

"Ukrainian forces are moving forward. Despite everything, and no matter what anyone says, we are advancing, and that is the most important thing. We are on the move," Zelenskiy wrote on the Telegram messaging app.

Some fear the West's support could begin to falter as colder and wetter weather slows progress on the battlefield later in the year. The West has poured in many billions of dollars to help the counteroffensive and Kyiv says it needs more.

Ukrainian battlefield momentum has picked up slightly in one part of the southeastern Zaporizhzhia front where Deputy Defence Minister Hanna Maliar said on Friday that Kyiv's troops had broken through the first line of Russian defences.

The White House said there had been "notable success" by Ukraine in the area, although Maliar warned that Kyiv's troops had reached even more heavily fortified positions on the other side after breaking through.

In its daily battlefield update, the Ukrainian military reported no new breakthroughs, but said its troops continued to advance towards Melitopol, a major Russian-occupied urban centre in Zaporizhzhia region.

It reported 45 combat clashes on the frontlines in the past 24 hours and said fighting raged in the east where Ukrainian troops had repelled multiple Russian attacks.

Russia has already described the Ukrainian counteroffensive as a failure. Kyiv says it has been advancing slowly on purpose to minimise losses, and its advance has been greatly complicated by its lack of modern air power.