Zelenskiy calls on G7 leaders to help end war in Ukraine by winter

It would be part of a package including ammunition for artillery and counter-battery radar systems. Overall, he said the US was now providing a total of $7.5bn (£6.1bn) in economic assistance each month. The proposed air defence system critical to help defend big cities such as Kyiv will be one of many pledges of military support being offered to Ukraine, either at the G7 or at the subsequent Nato defence summit in Madrid.

Germany is sceptical that the plan is workable and doubts if it would win sufficient support.

It said it was up to Ukraine to decide on a future peace settlement, free from external pressure or influence, but that the group stood ready to support an international reconstruction plan, drawn up and implemented by Ukraine in coordination with partners.

On the increasingly urgent problem of how to move Ukrainian grain being blockaded by Russia, one idea discussed at the summit, a UK source said, was a Dunkirk evacuation-style idea of seeking smaller-scale methods such as trucks and canal boats, rather than relying purely on container ships.

Ukraine claims that on Saturday alone 62 Russian rockets and missiles hit the country, including from the territory of Belarus. The southern port of Odesa was struck overnight and, hours before the G7 summit opened, the capital, Kyiv, was hit by its first strike since early June, in what was taken as a brutal message of defiance.

The US missile defence briefings did not clarify when Ukraine would receive the system, the degree of training required and to what extent it would receive the corresponding missiles. The US has to balance the need to show its commitment to the Ukrainian cause with a degree of military secrecy.

The long-awaited American Himars missile system is already on the Ukrainian frontline and being used to attack convoys of Russian equipment.

Johnson has been sending out ever fiercer warnings in advance of the summit discussion on Ukraine that Putin is poised to get away with the annexation of the country. The UK prime minister has refrained from criticising Germany in public, pointing to the extent of the German psychological journey from one of near pacifism to a preparedness to provide weaponry to Ukraine.