The United States and its allies will meet once a month to discuss Ukraine's defence needs to battle invading Russian troops, US Defence Secretary Lloyd Austin said Tuesday.

"Today's gathering will become a monthly Contact Group on Ukraine's self-defence," Austin said following the first session of a weapons summit.

"The Contact Group will be a vehicle for nations of goodwill to intensify our efforts, coordinate our assistance, and focus on winning today's fight and the struggles to come," he added.

Forty nations joined Tuesday's meeting at the Ramstein US airbase in southwestern Germany, including NATO members but also countries such as Israel, Japan and Australia. 

At the start of the talks, Austin had said Washington would "move heaven and earth" to help Ukraine win its battle against Russia's unprovoked invasion.

German Defence Minister Christine Lambrecht meanwhile announced that Berlin has agreed to give the go-ahead to the delivery of used Gepard (Cheetah) anti-aircraft tanks to Ukraine.

Austin praised the "major decision" by Berlin to supply the 50 anti-aircraft systems, and added that Canada would also send eight armoured vehicles.

"That's important progress. We're seeing more every day," he said.

"We don't have any time to waste. We've got to move at the speed of war."

Austin also reiterated that Washington wants Russia weakened militarily to prevent Moscow from threatening its neighbours.

Moscow has lost "a lot of equipment", noted Austin, pointing out that sanctions imposed by allies on Russia meant that it would not be easy for the country to replace some of its lost capabilities.

"We would like to make sure again that they don't have the same type of capability to bully their neighbours that we saw at the outset of this conflict," he said.