Dozens of Nato's modern battle tanks are to be sent to Ukraine to bolster the country's forces in their fight against Russia's invasion as the US and Germany confirm they will send supplies of the heavy fighting vehicles.
The US says it will send 31 Abrams tanks to Ukraine, reversing claims they are unsuitable for use in the war with Russia.
Germany confirmed it will provide Ukraine with Leopard 2 battle tanks and approve requests by other countries – such as Poland – to do the same.
In response to Germany’s announcement, UK Prime Minister Rishi Sunak tweeted: "The right decision by Nato allies and friends to send main battle tanks to Ukraine.
"Alongside Challenger 2s, they will strengthen Ukraine's defensive firepower.
"Together, we are accelerating our efforts to ensure Ukraine wins this war and secures a lasting peace."
The PM spoke to Mr Scholz and US president Joe Biden as the tank announcements were made, in a group call with French president Emmanuel Macron and Italian prime minister Giorgia Meloni.
Mr Sunak said that "decisive, collective action would be a catalyst for other countries to follow suit", according to Downing Street.
"The Prime Minister said it was now clear Russia was on the back foot, and there was a window for international partners to accelerate efforts to secure lasting peace for Ukraine.
"He called on allies to intensify their support in the coming weeks and months," a spokeswoman said.
Russian ambassador to Germany Sergey Nechayev on Wednesday called Berlin's decision to send Leopard 2 tanks to Ukraine "extremely dangerous", while a Kremlin spokesman said Western tanks will "burn" on the battlefields of Ukraine.
Germany had previously said the Leopards would not be sent unless the US put its Abrams on the table.
The UK became the first Western nation to promise main battle tanks, with Prime Minister Rishi Sunak announcing 14 Challenger 2s would be sent earlier this month.
Altogether, France, the UK, the US, Poland, Germany, the Netherlands and Sweden will send hundreds of tanks and heavy armoured vehicles to fortify Ukraine as it enters a new phase of the war and attempts to break through entrenched Russian lines.
Germany's decision to supply Leopard 2s comes after difficult negotiations.
Other allies operating the German-made Leopard 2 needed permission from Berlin to send them to the Ukrainians, something German Chancellor Olaf Scholz was reluctant to authorise unless the US also committed tanks.
The pressure on Mr Scholz mounted after Poland formally asked Germany to approve sending Leopard 2 tanks from Polish stocks to Ukraine.
The long-awaited decision in Berlin followed US officials saying a preliminary agreement had been struck for the United States to send its M1 Abrams.
The German government said it would initially provide Ukraine with one company of Leopard 2 A6 tanks – 14 vehicles – from its own stocks.
The goal is to provide Ukraine with a total of two battalions – 88 Leopard tanks – with donations from other countries.
Until now, the US has resisted providing its own M1 Abrams tanks to Ukraine, citing extensive and complex maintenance and logistical challenges with the high-tech vehicles.
Washington believes it would be more productive to send German Leopards since many allies have them and Ukrainian troops would need less training than on the more difficult Abrams.
For the Abrams to be effective in Ukraine, its forces will require extensive training on combined arms manoeuvre – how the tanks operate together on the battlefield, and on how to maintain and support the complex, 70-ton weapon.
The Abrams tanks use a turbine jet engine to propel themselves which burns through at least two gallons a mile regardless of whether they are moving or idling, which means that a network of fuel trucks is needed to keep the line moving.
Meanwhile, the UK Ministry of Defence said in its intelligence update on Wednesday that Russian troops in Ukraine were reluctant to accept T-14 main battle tanks because they were in such poor condition.