Ukrainian President Volodymyr Zelensky has said he will meet with two top American officials in Kyiv on Sunday.
Mr Zelensky gave few details about the logistics of his talks with US Secretary of State Antony Blinken and US Defense Secretary Lloyd Austin.
But he told reporters he expected results – "not just presents or some kind of cakes, we are expecting specific things and specific weapons".
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The visit would be the first to Kyiv by high-level US officials since the invasion began on 24 February.
While visiting Poland in March, Mr Blinken stepped briefly onto Ukrainian soil to meet with the country's foreign minister.
Mr Zelensky's last face-to-face meeting with a US leader was on 19 February in Munich, with Vice President Kamala Harris.
Russia has been trying to take Mariupol for nearly two months, and the city on the Sea of Azov has seen some of the war's worst deprivations.
Its capture would deprive Ukraine of a vital port, free up Russian troops to fight elsewhere, and establish a land corridor to the Crimean Peninsula, which Moscow seized in 2014.
Some 2,000 troops have been fighting tenaciously to hold on to the last remaining Ukrainian outpost in the city, the Azovstal steel plant, which also has civilians taking refuge in its labyrinthine tunnel system.
Watch: Update on the latest weapons kit sent from the West to support Ukraine.
Russian forces have continued to pummel the plant, hitting it with air strikes, including by long-range aircraft, Oleksandr Shtupun, spokesman for the Ukrainian Armed Forces General Staff, said on Sunday.
Russia has also pressed its attacks elsewhere in the eastern Donbas region, where Moscow-backed separatists controlled some territory before the war and the Russians are aiming to gain full control over Ukraine's eastern industrial heartland.
Russia has pulled back forces from Ukraine's capital, Kyiv, and the north of the country to feed into the Donbas offensive, but the British Ministry of Defence said on Sunday that Ukrainian forces had repelled numerous assaults in the past week.
"Despite Russia making some territorial gains, Ukrainian resistance has been strong across all axes and inflicted significant cost on Russian forces," the ministry said in an intelligence update.
"Poor Russian morale and limited time to reconstitute, re-equip and reorganise forces from prior offensives are likely hindering Russian combat effectiveness," it said.