NATO Secretary General Jens Stoltenberg said on Thursday Russia was coming under heavy pressure in Ukraine after Moscow ordered the withdrawal of its troops from the southern city of Kherson.

Speaking after meeting Italian Prime Minister Giorgia Meloni, Stoltenberg said NATO would be watching in the coming days to see if the Russians did indeed pull back from the west bank of the Dnipro River.

"What is clear is that Russia is coming under heavy pressure and if they leave Kherson it would be another victory for Ukraine," Stoltenberg told reporters after talks with new prime minister Meloni.

He added that NATO would support Ukraine "for as long as it takes."

"The unprecedented support that NATO allies, including Italy, has provided is making a difference on the battleground every day and remains vital for the Ukrainian progress," he told reporters.

Meloni, who took office last month, said her government remained committed to defending "the territorial integrity, sovereignty and freedom of Ukraine."