“We strongly believe that we will succeed,” Zelensky told the Wall Street Journal.

“I don’t know how long it will take. To be honest, it can go a variety of ways, completely different. But we are going to do it, and we are ready.”

Kyiv hopes a counter-offensive to reclaim territory will change the dynamics of the war that has raged since Russia invaded its smaller neighbour 15 months ago.

Zelensky said last month Ukraine needed to wait for more Western armoured vehicles arrived before launching the counter-offensive. He has been on a diplomatic push to maintain Western support, seeking more military aid and weapons, which is key for Ukraine to succeed in its plans.

Russia holds swaths of Ukrainian territory in the east, south and southeast.

A long spell of dry weather in some parts of Ukraine has driven anticipation that the counter-offensive might be imminent. Over the past several weeks Ukraine has increased it strikes on Russian ammunition depots and logistical routes.

On Saturday Ukraine’s military said in a daily report that Mariinka in the Donetsk region in the east was the focus of fighting. Ukrainian forces repelled all 14 Russian troops’ attacks there, the report said.