Ukrainian president Volodymyr Zelenskiy has paid another visit to troops on the front lines of Ukraine's war against Russia, praising soldiers holding forward positions as brave and hard-working and vowing the country will prevail.

A video posted to Zelenskiy's official Telegram account on Saturday showed the president in his trademark khaki t-shirt, handing out medals and posing for selfies with the troops in what appeared to be an underground shelter in the southern Mykolaiv region.

The president's office did not say when he made his latest trip to see troops.

"Our brave men and women. Each one of them is working flat out," Zelenskiy said in the video. "We will definitely hold out! We will definitely win!"

Zelenskiy has remained mostly in Kyiv since Russia invaded the country on Feb 24. But in recent weeks he has made unannounced visits to the northeastern city of Kharkiv, where there had earlier been heavy fighting, and to two eastern cities close to where battles are being fought.

There is also fighting on the eastern and southern edges of the Mykolaiv region in south Ukraine.

Zelenskiy's office said the president also visited the regional capital Mykolaiv and inspected its destroyed administration building, where 37 people were killed in late March when a missile blasted through the building.

Russian forces reached the outskirts of Mykolaiv in early March but were driven back.

He also visited a hospital in Mykolaiv and awarded honours for bravery to Mayor Oleksandr Senkevych and Governor Vitaliy Kim for their work during the four months of Russia's invasion, his office said in separate statements.

His office underscored the strategic importance of the territory, which borders the Russia-occupied Kherson region.

"Mykolaiv region is a bridgehead for the liberation of the Kherson region, which is a goal for every one of us," said Chief of Staff Andriy Yermak on Telegram.

His office later said Zelenskiy had also visited National Guard positions in the Odesa region, where he thanked the troops for their service, saying: "As long as you live, there is a strong Ukrainian wall that protects our country."

Moscow says it is engaged in a "special military operation" to disarm its neighbour. Ukraine and its allies say Moscow has launched an unprovoked war of aggression, killing thousands of civilians and flattening cities.

- Reuters