"We are not going to send to Ukraine rocket systems that can strike into Russia," Biden told reporters in Washington.

Pro-Western Ukraine has received extensive US military aid since Russia invaded its neighbor in late February, but says it needs long-range rockets equivalent to what Moscow's forces use.

Kyiv has asked the United States for mobile batteries of long-range rockets, the M270 MLRS and the M142 Himars, which can launch multiple rockets at the same time with a range of up to 187 miles (300 kilometers), eight times or more the distance of artillery in the field.

This could give Ukrainian forces the ability to reach, with great precision, targets far behind Russian lines, though it is unclear if that is their intent.

"If the West really wants Ukraine's victory, maybe it is time to give us long-range MLRS?" Ukrainian President Volodymyr Zelensky's advisor Mykhailo Podoliak tweeted recently.

"It is hard to fight when you are attacked from a 70 km (43 miles) distance and have nothing to fight back with."

The United States earlier in May announced another $40 billion assistance package amid speculation it included such weapons.

Since failing to capture Kyiv in the war's early stages, Russia's army has narrowed its focus, hammering cities with relentless artillery and missile barrages as it seeks to consolidate its control.

Moscow's forces have continued a push in the eastern Donbas region, upping the pressure on the twin cities of Severodonetsk and Lysychansk.

Ukrainian forces pushed back over the weekend in the southern region around Kherson as Zelensky seeks to crank up already hefty international pressure on Moscow.