The United States is set to send more aid to Ukraine, most of it ammunition for equipment such as HIMARS rocket launchers, before an anticipated Russian assault this spring.

At a press briefing in Washington on Thursday, John F. Kirby, the National Security Council spokesman, declined to give details on the size of the new aid package and did not offer a timeline for when it would be delivered. More information is expected to be released on Friday, he said.

Ukraine is running low on ammunition after a year of fighting Russia. The world’s biggest producers of ammunition cannot keep up with the pace of fighting, which is straining global arms production. Ukraine’s allies, including NATO members, are moving billions of dollars of equipment to Ukraine but are hampered by a patchwork of rules and the desire to replenish their own stockpiles.

Last week, the Pentagon said that it would spend $2 billion on equipment for the Ukrainian military so the country could sustain its long-term needs. The United States will buy that equipment, which includes ammunition for artillery and long-range rocket systems, from manufacturers instead of drawing from its own stockpile. That will delay the delivery by months or years.

With last week’s offering, Washington has provided $32 billion in military aid to Ukraine since February 2022.