"We have to see how the situation on the ground develops in the coming days. But what is clear is that Russia is under heavy pressure and if they leave Kherson, it would be another victory for Ukraine," he said in Rome.

Ukraine said Thursday its forces had reclaimed a dozen villages in the southern Kherson region, a day after Russia ordered its troops to withdraw from the eponymous city.

"We have seen how the Ukrainian armed forces have been able to push back Russian forces and liberate territory," Stoltenberg said.

"These gains belong to the brave courageous soldiers of Ukraine.

"At the same time the unprecedented support that NATO allies, including Italy, have provided is making a difference on the battlefield every day and remains vital for the Ukrainian progress."

Stoltenberg was speaking after his first face-to-face talks with Italian Prime Minister Giorgia Meloni, who took office late last month.

Her government allies include many people sympathetic to Moscow, although she herself has repeatedly emphasised her support for Ukraine and for sanctions against Russia.

Meloni said one of her priorities was to work to strengthen the alliance, to make it "even more capable of responding to threats coming from all directions".

"The alliance is indispensable for security and the prosperity of our countries," she told reporters.