The Biden administration announced on Tuesday that it will send Ukraine a small number of high-tech, medium-range rocket systems, a critical weapon that Ukrainian leaders have been begging for as they struggle to stall Russian progress in the Donbas region.

The rocket systems are part of a new $700 million tranche of security assistance for Ukraine from the U.S. that will include helicopters, Javelin anti-tank weapon systems, tactical vehicles, spare parts and more, according to two senior administration officials. The officials spoke on the condition of anonymity to preview the weapons package that will be formally unveiled on Wednesday.