Sunday's visit, announced by Ukrainian President Volodymyr Zelenskiy on Saturday, would be the highest-level visit by US officials to the country since the start of the war on February 24.

The White House has not confirmed any travel plans for Blinken and Austin. The State Department and Pentagon declined to comment.

As the war enters its third month, there is no end in sight to the fighting that has shocked the world, killed thousands, uprooted millions and reduced cities to rubble.

"Tomorrow we will discuss this exact list of weapons that are essential for us and the pace of deliveries," Zelenskiy told a dramatic Saturday evening news conference in an underground metro station.

"We would like to have... powerful heavy weapons. As soon as we have (more weapons), as soon as there are enough of them, believe me, we will immediately retake this or that territory, which is temporarily occupied."

Zelenskiy's comments came as Russia resumed its assault on defenders making a last stand in a giant steel works in Mariupol, days after Moscow declared victory in the key southern port city and said its forces did not need to take the plant.

The attack on Mariupol, the biggest battle of the conflict, has raged for weeks. Capturing the city is seen as vital to Russia's attempts to link the eastern Donbas region with Crimea, the Black Sea peninsula Moscow seized in 2014.

Moscow-backed separatists have for years held territory in the Donbas region, which contains the areas of Donetsk, including Mariupol, and Luhansk.

Luhansk Governor Serhiy Gaidai noted that fighting was continuing on the Orthodox Easter holiday.

"Usually we would come to our churches with Easter baskets. But now this is impossible," Gaidai posted on his Telegram channel. "Seven churches in Luhansk region have been mutilated by Russian artillery."

Reuters could not independently verify the report of the destroyed churches.

Ukraine estimates tens of thousands of civilians have been killed in Mariupol and says 100,000 civilians are still there. The United Nations and Red Cross say the civilian toll is at least in the thousands.

A new attempt to evacuate civilians failed on Saturday, an aide to Mariupol's mayor said.

Oleksiy Arestovych, a political adviser to Zelenskiy, said Ukrainian troops in the steel complex were holding out and attempting counterattacks. More than 1000 civilians are also in the plant, according to Ukrainian authorities.

Ukraine's military said on Sunday that Russian forces were continuing their offensive in the east of the country to establish full control over Donetsk and Luhansk, and ensure a land route to the annexed Crimea peninsula, adding they were attacking both military and civilian infrastructure.

It said Russian forces were also partially blockading the northeastern city of Kharkiv, and had moved Iskander-M missile launchers some 60 km from the Ukrainian border. The Iskander-M system fires short-range ballistic missiles that can hit targets 500 km away.

In Donetsk and Luhansk, Ukrainian forces said they repulsed 12 attacks on Saturday, destroying four tanks, fifteen units of armoured equipment and five artillery systems, among others. Reuters could not independently confirm the reports.

In the Black Sea port of Odesa, at least eight people were killed, Zelenskiy said on Saturday. Two missiles struck a military facility and two residential buildings and two more were destroyed, the Ukrainian armed forces said.

The death toll could not be independently verified. The last big strike on or near Odesa was in early April.

Russia has denied targeting civilians in its "special military operation".

The Russian defence ministry said it used high-precision missiles to destroy a logistics terminal in Odesa containing weapons supplied by the United States and European nations.

Australian Associated Press