The US will send $300m (£234m) in military weapons to Ukraine, including ammunition, rockets and anti-aircraft missiles, the White House has said.
The surprise announcement comes as a bill in Congress to send further aid to Ukraine stalls amid partisan debate.
The US shipment, the first in nearly three months, is intended to prevent Ukraine from losing ground to Russia.
National Security Adviser Jake Sullivan said this aid “is nowhere near enough to meet Ukraine’s battlefield needs”.
“This ammunition will keep Ukraine’s guns firing for a period, but only a short period,” Mr Sullivan told reporters on Tuesday, adding that “it will not prevent Ukraine from running out of ammunition.”
The White House had a budget previously approved by Congress for Pentagon operations, and that budget was not fully expended due to internal cost savings, giving the WH room to reallocate some of it. But this is just a drop in the bucket, Congress needs to act on the larger support package and provide dedicated funds for the effort.