ASHINGTON (AP) — The Biden administration says 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, two senior administration officials said Tuesday. The officials spoke on the condition of anonymity to preview the weapons package that will be formally unveiled on Wednesday.

The U.S. decision to provide the advance rocket systems tries to strike a balance between the desire to help Ukraine battle ferocious Russian artillery barrages while not providing arms that could allow Ukraine to hit targets deep inside Russia and trigger an escalation in the war.

In a guest essay published Tuesday evening in The New York Times, President Joe Biden confirmed that he's decided to “provide the Ukrainians with more advanced rocket systems and munitions that will enable them to more precisely strike key targets on the battlefield in Ukraine.”

Biden had said Monday that the U.S. would not send Ukraine “rocket systems that can strike into Russia.” Any weapons system can shoot into Russia if it's close enough to the border. The aid package expected to be unveiled Wednesday would send what the U.S. considers medium-range rockets — they generally can travel about 45 miles (70 kilometers), the officials said.