Liz Truss has appeared to backtrack on a call for Ukraine to be sent war planes to boost its fight against Russia – saying she only wants “plane parts” to be delivered.

       In a speech today, the foreign secretary will say: “Heavy weapons, tanks, aeroplanes – digging deep into our inventories, ramping up production. We need to do all of this,” according to an advance briefing.

       But the call would amount to a major reversal of Nato policy so far, which has seen the US reject a Polish plan to deliver fighter jets for fear of provoking a wider conflict with Vladimir Putin.

       Dominic Raab, the deputy prime minister, failed to back a rethink, saying only that the West should “listen very carefully to what the Ukrainians need”.

       However, it is understood that Ms Truss is not calling for the UK to send fighter planes, but will back Washington’s existing drive to ensure “plane parts” reach Ukraine.

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       She will argue it is “legitimate” for other Nato countries to send planes should they wish to do so, an option that “should be on the table”.

       The clarification comes after the foreign secretary was embarrassed over her backing, at the start of the war, for British mercenaries to join the fight in Ukraine.

       The idea was quickly dismissed by other ministers – and Ms Truss tried to deny advocating it, despite giving her support in a TV interview.

       The confusion follows a warning from a senior Conservative that Boris Johnson is failing to explain what is “mission success” in Ukraine, as the war drags on into its third month.

       Tobias Ellwood, a former defence minister, said Nato’s policy must be to force Russia out of the eastern Donbas region, where experts fear a long bloody stalemate now looms.

       “The unanswered question I hope the foreign secretary will address is ‘what are we collectively trying to achieve? What is mission success’?” he said.

       In a major speech this evening, Ms Truss will warn that the world “will never feel safe again” if Putin is allowed to win in Ukraine.

       She will call for higher defence spending across the West, saying: “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.

       “Heavy weapons, tanks, aeroplanes – digging deep into our inventories, ramping up production. We need to do all of this,” the briefing read.

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       Asked if he agreed with sending war planes, Mr Raab said only: “I certainly don’t think we should be avoiding providing support to Ukraine at this critical moment in the war. And the Foreign Secretary is right about that.”

       Pressed on providing planes specifically, he added: “We need to listen very carefully to what the Ukrainians need and help with our allies to provide them with the military support, so that they win and so that Putin loses, and that’s part of it, so is the sanctions.”