Lloyd Austin, the US defence secretary, has said the west was gearing up to help Ukraine for “the long haul” and would take steps to boost rearmament to help the embattled country following a meeting of defence ministers in Germany.

Politicians present also discussed coordinating future arms supplies on top of $5bn (£3.9bn) already committed, but the growing effort has already prompted Russia to accuse the west of engaging in “a proxy war” by arming Ukraine against Moscow.

“We have an important session today on the long term support for Ukraine’s defence including what that will take from our defence industrial bases,” Austin said after a 40-country meeting at the Ramstein airbase in south-west Germany.

The secretary added that that would mean “dealing with the tremendous demand that we’re facing for munitions and weapons platforms” and “redoubling our common efforts to strengthen Ukraine’s military for the long haul”.

Western allies have been stepping up their arms supply to Ukraine, in response to pleas from the country’s president, Volodymyr Zelenskiy, to turn the tide in the fighting, leading to escalating Russian criticism as the war continues.

Late on Monday, the Russian foreign minister, Sergei Lavrov, accused Nato of being “engaged in a war with Russia through a proxy and is arming that proxy” in response to a question about whether the current situation could be compared to the Cuban missile crisis that nearly caused a nuclear war.

In response, Austin said on Tuesday that both Ukraine and the west would “do everything in our power” to ensure the war does not “spin out of control”. He added: “Bluster about the use of nuclear, the possible use of nuclear weapons is very dangerous and unhelpful. Nobody wants to see a nuclear war, nobody can win it.”

A key ally of President Vladimir Putin, Nikolai Patrushev, the head of Russia’s security council, on Tuesday said the outcome of “the policies of the west and the Kyiv regime controlled by it would only be the breakup of Ukraine into several states” – an apparent attempt to blame the west for supporting the Zelenskiy government.

At the western conference, Germany promised it would send approximately 50 refurbished Gepard anti-aircraft missile launchers, leading to praise from the Pentagon chief after weeks of pressure on Berlin to step up its supply of heavy weaponry.

It was “a major decision” said Austin. “I think those systems will provide real capability to, for Ukraine,” he said, and added he believed the country’s defence minister, Christine Lambrecht, would “continue to look for ways to be relevant and provide the good capability to the Ukrainians”.

Britain pledged a day earlier to send “a small number” of Stormer vehicles which carry Starstreak anti-aircraft missiles – while Canada said at the conference it would send eight armoured vehicles to help Ukraine. But there was no announcement of any commitment to send tanks.

Although Nato has repeatedly said it will not enter the war to fight against Russia, western politicians have begun to say their goal is help Ukraine decisively defeat to its neighbour, so that it cannot threaten Kyiv or other neighbours.

Earlier this week Austin said that Russia should be “weakened to the point where it can’t do things like invade Ukraine” and when asked again about that statement on Tuesday, he offered a similar formulation.

“We would like to make sure again, they don’t have the same type of capability to bully their neighbours that we saw at the outset of this conflict,” he said, highlighting that Russia’s “land forces have been attrited in a very significant way, casualties are pretty substantial, they’ve lost a lot of equipment.”

Prior to the meeting, the US said that the total value of arms donated to Ukraine was $5bn, with the US accounting for $3.7bn. On Monday, the UK said it had already sent £200m worth of arms and had a budget to supply £500m if needed.

The UK foreign secretary, Liz Truss, said in a major speech on Tuesday night that the west will never feel safe again and Europe will experience untold further misery if Putin succeeds in Ukraine.

“We cannot be complacent – the fate of Ukraine remains in the balance. And let’s be clear – if Putin succeeds there will be untold further misery across Europe and terrible consequences across the globe. We would never feel safe again. So we must be prepared for the long haul and double down on our support for Ukraine,” she said in the foreign secretary’s annual Mansion House speech.

Truss, still seen as a frontrunner for the Conservative leadership if Boris Johnson resigns, called for a “recasting and rebooting” of the global security architecture “since it has failed Ukraine”, arguing the conflict could be a catalyst for change in the way the free world deters global aggressors.

“I want to live in a world where free nations are assertive and in the ascendant … where freedom and democracy are strengthened through a network of economic and security partnerships … where aggressors are contained and moving toward a better path. This is the long-term prize: a new era of peace, security and prosperity.”