The Ukrainian president has appealed to more western allies to speed up the delivery of military support – including badly needed heavy armour – in his country's struggle against invading Russian forces.
In an address to a pledging conference at the US airbase in Ramstein, Germany, Volodymyr Zelensky urged assembled defence ministers to agree in "principle" to supply his forces with modern battle tanks.
So far, among the Nato allies, only the UK has agreed to send tanks, in the form of 14 British Army Challenger 2s.
Mr Zelensky's call will intensify the pressure on Germany to authorise the release of its Leopard 2 battle tanks, which are potentially available in far greater numbers.
Speaking remotely from Ukraine, Mr Zelensky thanked allies for their previous support but said "hundreds of thank yous are not hundreds of tanks".
"We have to speed up. Time must become our weapon, just like air defence and artillery, armoured vehicles and tanks, which we are negotiating about with you and which will actually make a victory," he said.
"You can start this policy today. It is in your power to make a Ramstein of tanks. Not to bargain about different numbers of tanks but to open (the) principle (of) supply that will stop Russian evil."
Mr Zelensky's plea for greater speed was echoed by US defence secretary Lloyd Austin, who convened the talks and said the conflict has reached a "decisive moment".
"Russia is regrouping, recruiting and trying to re-equip. This is not a moment to slow down. It is a time to dig deeper," he said.
The UK's Defence Secretary also appealed to allies to keep up the pressure on Moscow on the battlefield.
"The UK is leading international support for Ukraine by becoming the first nation to donate modern, Western main battle tanks," Ben Wallace said in a statement.
"It is crucial that we build on this momentum supported by our international partners, who are determined like us, to ensure that Putin's illegal and unprovoked invasion fails."
The Ukrainians are seeking around 300 tanks to enable them to mount a counter-offensive, with the German-built Leopard 2s – which are widely used by European armies – seen as the most suitable candidate.
Poland has offered to send a company of its Leopard 2s, but requires a sign-off from Berlin, which issued the original export licences, if they are to be re-exported.
So far, however, the government of Chancellor Olaf Scholz has been reluctant to do so amid concerns about the likely reaction in Moscow.
Reports have suggested the Germans would be prepared to relent if the US was to release some of its Abrams tanks.
The Americans, however, argue that the Abrams is a more complex machine – requiring more training for crews – while their turbine engines are heavy on fuel, making them unsuitable for Ukraine's beleaguered forces.
Amid growing impatience in Kyiv and among some allies, Poland's prime minister Mateusz Morawiecki has suggested he would be willing to send Leopard 2s without Germany's consent.
"We will either obtain this consent quickly, or we will do it ourselves," he told Polish radio.
Ahead of the Ramstein gathering, US defence secretary Mr Austin met new German defence minister Boris Pistorius in Berlin on Thursday, but there was no immediate sign of any breakthrough.
Mr Wallace said that in addition to its latest support package, including the Challenger 2s and other heavy armour, the UK would be sending a further 600 Brimstone precision-guided missiles.
The US on Thursday announced a $2.5bn (£2bn) Ukraine aid package which includes 90 Stryker combat vehicles, 59 Bradley fighting vehicles and hundreds of thousands of rounds of ammunition.
The more heavily armoured and tracked Bradleys and the medium-armoured Strykers will provide Ukraine "with two brigades of armoured capability", the Pentagon said in a statement.
Meanwhile, Foreign Secretary James Cleverly said the UK will join international allies in considering plans for a new tribunal to deal with alleged war crimes committed by Russian forces.
The Government has accepted an invitation from Kyiv to join a "core group" of nations looking at the feasibility of setting up a "hybrid" tribunal, which would be integrated into Ukraine's national justice system but with international elements.
"The atrocities we've witnessed in Ukraine are diabolical – thousands of soldiers and civilians killed, and millions more displaced, forced to flee for their lives in the most horrific circumstances. These atrocities must not go unpunished," Mr Cleverly said.