The $3bn security package — first reported by the Associated Press, citing US officials — would be the largest amount of military aid Washington has provided to Ukraine since Russia launched its assault on February 24.
It would also signify a shift to a longer-term strategy, with the money providing funding contracts for drones and other equipment that may not see the battlefield for at least a year, the officials told AP.
Previous shipments have focused on Ukraine's immediate needs of weapons and ammunition, and included items that the Pentagon already had in stock.
The expected announcement comes as US reports showed Russia may be preparing to ratchet up attacks on civilian infrastructure and government facilities before Ukraine's Independence Day on Wednesday.
Americans in the country have been advised to depart immediately using their own means if able to do so.
Ukrainian President Volodymyr Zelenskyy said he believes Russian troops could attempt “something particularly ugly” this week.
In addition to providing security assistance for Ukraine's long-term defensive needs, the package is intended to reassure Ukrainian officials of US support.
Six months after Russia invaded Ukraine, the war has ground to a stalemate, as both sides trade small advances in the east and south. Both nations have suffered thousands of casualties, and countless civilians have been killed by Russian bombing.
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The US has provided about $10.6bn in military aid so far. American defence leaders are also considering plans to expand training for Ukrainian troops outside their country.
Germany has also stepped up plans to provide more anti-drone devices, ammunition and recovery vehicles as part of a new package announced by Chancellor Olaf Scholz. The planned shipment will be worth more than $500 million, Bloomberg reported.
The Associated Press contributed to this report