The European Union is urgently exploring ways for member states to collectively buy munitions to help Ukraine, following warnings from Kyiv that its forces rapidly need more supplies.
The bloc's foreign affairs ministers met in Brussels on Monday where they discussed the idea of joint arms purchases.
But Josep Borrell, the EU's top diplomat warned that this would take time, even if Ukraine has urgent needs, and collective acquisition of supplies should be considered.
"It is evident that we have to intensify our joint efforts notably through possible procurements at European level to address Ukraine's urgent needs," the High Representative for Foreign Affairs told reporters after the ministerial meeting.
"But it is also clear that in the next weeks the best way to provide ammunition to Ukraine is to share the already existing ammunition stockpiles of the European armies.
"We don't have to wait for them to be produced. We have to use what has already been produced in a stockpile or has already been contracted and will be produced in the coming days," he added.
Over the weekend at the Munich Security Conference, Ursula von der Leyen said that a joint arms buying scheme could be similar to the EU's advance purchase of COVID vaccines, where the European Commission acted on behalf of all member states to collectively secure jabs to fight the disease.
The idea of joint procurement of 155-millimetre artillery shells – badly needed by Kyiv – is a proposal first submitted by Estonia.
For Urmas Reinsalu, Minister of Foreign Affairs for Estonia, it is not acceptable to make Ukraine wait so long for supplies.
"The cost would be €4bn and if you look to compare the figures today, this is a situation where as much shells Russia uses daily, the European Union produces per month and in the current military industry capabilities," Reinsalu told journalists in Brussels.
"We can reach the need of Ukraine in around six years and this is fully unacceptable."
He added that member states should transfer their stockpiles to Kyiv as soon as possible.
"I would urge all the countries who still have amounts of shells in their possessions to consider immediately they give it to Ukraine," he said.
Josep Borrell also said that a tenth package of sanctions against Russia should be adopted before the end of this week when Ukraine will mark one-year anniversary of Moscow's invasion.