The UK foreign secretary has justified the supply of Challenger tanks to Ukraine, saying it was designed to bring the war to a quick conclusion and there was a moral imperative to end the war soon due to the casualties and cost. “This war has been dragging on for a long time already. And now is the time to bring it to a conclusion,” James Cleverly told a Washington thinktank. His remarks seemed designed both to encourage the US to step up its own weapons supply, and to push back against those Republicans calling for US support for the war to be scaled back. Before meeting with the US secretary of state, Anthony Blinken, Cleverly said it was clear Putin believed Russian stoicism could outlast the west and that he wanted to drag out an attritional conflict, so it was incumbent on the west to apply the opposite strategy. He said: “We should look to bring it to a conclusion quickly, the conclusion has to be Ukrainian victory. And that dictates therefore that we need to intensify our support at this point in time, while Russia has been on the back foot.” He later added it was a moral imperative to do so since “it will cost so much more in human lives and so much more in money, if we allow this to be a long, drawn out attritional war. “What Putin should understand is we are going to have the strategic endurance to stick with them until the job is done and the best thing that he can do to preserve the lives of his own troops is to recognise that.” Cleverly is visiting the US and Canada after Britain became the first country to meet Ukraine’s request for western heavy tanks. UK prime minister, Rishi Sunak, said his government would provide 14 Challenger 2 tanks. European countries have previously supplied Kyiv with modernised versions of Soviet tanks and the US and France have committed to lighter versions, with Washington sending Bradley armoured vehicles. Cleverly joined the UK defence secretary, Ben Wallace, in calling for Germany to permit the supply of Leopard 2 tanks to Ukraine. Cleverly said that Britain had decided to send tanks to the Ukrainians because “what we recognise they need is the ability to push back hard in the east and in the south”, areas which Russia has tried to seize since its invasion was launched nearly a year ago. He refused to say whether he wanted the US to supply more weapons, such as the ACTMS or air cover, but added: “Our support has evolved as the battle has evolved, and as the requirements of the Ukrainians have evolved.” He said it was really key for US citizens to recognise that the Ukraine war was about “keeping them safe. If the postwar framework fell apart the world becomes a much more dangerous, chaotic and expensive place”. Later, at a joint press conference with Blinken at the state department, Cleverly again praised the US contribution to Ukraine’s war effort. “We should never lose sight of the fact that the United States of America is the single largest donor of military and economic aid to support Ukraine’s self-defence of any country in the world,” he said. “The UK is very proud to be number two in that pecking order.” He added: “I think it’s really important the American people recognise what their own government is doing in support of freedom and opposition to this aggression and oppression.” Blinken said the US applauded the UK’s decision to send Challenger tanks. Pressed on Germany’s reluctance to allow the supply of tanks unless American tanks are sent first, the secretary of state insisted: “On the question of tanks, or for that matter any weapons system, these are sovereign decisions for each country to make. I would note that what Germany has done to date has been quite extraordinary.” Blinken said the US had provided $25bn (£20bn) in security assistance to Ukraine in less than a year and anticipates more announcements in the next week as Lloyd Austin, the defence secretary, convenes another session of the Ukraine Defense Contact Group at Ramstein airbase in Germany. “So stay tuned for more on that,” he said. He added: “The bottom line is we are determined to make sure that Ukraine has what it needs to succeed on the battlefield. As we’ve said, the fastest way to bring this war to a just and durable end, to get to diplomacy, to get to a negotiation, is to give Ukraine a strong hand on the battlefield. That’s exactly what we’re doing.” Speaking in Davos the Polish president, Andrzej Duda, said it was important Russia did not get out of the war unscathed, adding he was confident that Germany would allow the supply of Leopard 2 tanks to a third party such as Ukraine. Germany as manufacturer of the tanks has to give permission to Nato countries for Leopards to be supplied to Kyiv. The German economy minister, Robert Habeck, said it would be easier for Germany if the US was also to supply tanks. The US operates thousands of M1 Abrams tanks built by General Dynamics, but some say they are unsuitable for Ukraine as they are driven by gas turbine engines.