Russian Deputy Prime Minister Marat Khusnullin has visited Mariupol, the country's most senior government official yet to set foot in the Ukrainian southern port city after weeks of Russian bombardment.

Russia, which sent thousands of troops into Ukraine on Feb. 24 in what it calls a special military operation, claimed taking control of the city on the Sea of Azov on April 21 after nearly two months of siege.

However, some Ukrainian fighters are still holed up in the city's vast Soviet-era Azovstal steelworks - the last holdout against Russian forces there. Ukrainian military said on Sunday Russia continued intensive shelling of the plant.

Khusnullin, who in the Russian government is in charge of construction and urban development, said on Telegram he had visited Mariupol and eastern Ukrainian town of Volnovakha among other territories "liberated" by Russian forces.

"Restoration of peaceful life begins in the regions. There's a lot of work to be done. We will help, in particular ... with providing humanitarian aid," he wrote in a Telegram post

Khusnullin visited the commercial port of Mariupol he said should be used to bring in building materials to restore the city, according to Russian defence ministry's TV channel Zvezda.

The port, which lies between the Crimea Peninsula seized by Moscow in 2014 and parts of eastern Ukraine taken by Russian-backed separatists the same year, is key to linking up the two Russian-held territories and blocking Ukrainian exports.

The port will ship off the first cargo from Russian-backed self-proclaimed Donetsk People's Republic in May, its head Denis Pushilin, who accompanied Khusnullin, said on Telegram.

Moscow says its actions in Ukraine are aimed to disarm Ukraine and rid it of what it calls anti-Russian nationalism fomented by the West.

Ukraine and the West say Russia launched an unprovoked war and have accused Russian forces of land grab and war crimes. Moscow denies the allegations and says it targets only military or strategic sites, not civilians.