The United Kingdom and Germany are leading a renewed push to provide air defense systems and ammunition to Ukraine, on the heels of a 50-day ultimatum given by U.S. President Donald Trump to his Russian counterpart Vladimir Putin.

“Together we have to stop this war machine by joining forces to support Ukraine with all our might,” German Defense Minister Boris Pistorius said Monday, ahead of a virtual meeting of the Ukraine Defense Contact Group (UDCG). “First and foremost, this requires us to urgently bolster Ukrainian air defense.”

On Sunday, Russia attacked Ukraine with more than 450 drones and missiles. Air defense forces managed to shoot down about half of them, with 23 drones hitting targets and damage reported in three locations in Kyiv, Kharkiv, and Ivano-Frankivsk regions. Two people were killed and 15 injured.

Earlier in July, Trump gave Putin 50 days to reach a ceasefire or face economic sanctions. The U.S. president, whose administration had temporarily halted some promised munitions for Ukraine, also agreed to sell American weapons to Europeans and let them donate them to Kyiv.

“We need to step up in turn to a 50 day drive to arm Ukraine on the battlefield,” said U.K. Defense Secretary John Healey as the group of allies, also known as the Ramstein format, met online on Monday.

London and Berlin — who have taken over the UDCG’s chairmanship from Washington since Trump came to power — announced that Germany would finance €170 million in U.K.-led procurement of air defense ammunition for Ukraine.

Germany will pay for and donate 220,000 rounds of 35-millimeter ammunition for the Gepard anti-aircraft gun system and procure long-range Ukrainian-made drones.

Europeans are also still working on a recent pledge to provide five Patriot air defense systems to Ukraine. “How we can achieve that is something we will coordinate closely … within the next few days,” Pistorius said, thanking Belgium, Denmark, Sweden and Norway for their involvement.

One of the main options on the table is for Europeans to give systems from their own stocks, that would then be backfilled with new orders to the U.S.

NATO’s Supreme Allied Commander Europe, General Alexus Grynkewich, will meet with some NATO representatives on Wednesday to discuss the issue.

Last week, the U.S. told Switzerland it would get military equipment later than planned because Washington will “reprioritize the delivery of Patriot systems to support Ukraine.” According to The Wall Street Journal, the move is designed to benefit Germany’s backfilling.