The White House unveiled a fresh package of arms and ammunition for Ukraine worth $1 billion, including coastal anti-ship defence systems and ammunition for artillery and advanced rocket systems.

Speaking in Brussels after a meeting with allies backing Kyiv, top US general Mark Milley insisted that Ukraine had in some cases received more tanks and artillery than requested.

Those included "97,000 anti tank systems, more anti-tank systems than there are tanks in the world".

He said the first of 10 long-range rocket artillery systems would be "in the fight" in a few weeks after an initial batch of Ukrainian troops were trained to use them.

"If they use the weapon properly, and it's employed properly, they ought to be able to take out a significant amount of targets, and that will make a difference," Milley said.

Milley said that Ukraine remains heavily outgunned by Russia's fire-power and estimates of 100 soldiers killed a day were "in the ballpark" with Washington's assessments.

"The Ukrainians on the other hand are using much better artillery techniques and they're having pretty good effect on the Russians," he said.

"The Russians have lost probably somewhere in the tune of 20 to 30 percent of their armoured force."

He said Kyiv's forces were in an existential fight for their country's future and the battle for the Donbas region was not "a done deal" despite the numbers favouring Moscow.

"Your ability to endure a suffering, your ability to endure casualties, is directly proportional to the object to be attained," Milley said.

"If the object can be attained is survival of your country, then you're going to sustain it."