President Volodymyr Zelensky acknowledged on Friday that Ukraine would not be able to join the Nato before the end of the Russian invasion.
Russia's invasion of Ukraine in February last year has galvanised the Western military alliance, set up almost 75 years ago, to face off against the Soviet Union.
However, members of the military bloc are split over Ukraine, with Nato chief Jens Stoltenberg saying that all members agree to stick by a 2008 pledge that Ukraine will become a member at some undefined point.
"We are reasonable people and we understand that we are not going to drag a single Nato country into a war," Zelensky said during a briefing along Estonian President Alar Karis.
"Therefore, we understand that we will not be members of the Nato while this war is going on. Not because we don't want to, but because it's impossible," he added.
Ukraine is a candidate to join both the North Atlantic Treaty Organisation (Nato) and the European Union but some European capitals are wary of setting a formal timeline for membership as Russia's invasion continues.
Joining the Nato would mean Ukraine would be covered by the alliance's Article 5 collective defence clause that obliges all members to help defend it if attacked.
Friday's comments were a rare admission by the Ukrainian president, who has stepped up pressure on the Nato and the European Union to open their doors to Ukraine since the beginning of Russia's invasion in February last year.
On Thursday, Zelensky told a summit in Moldova that any doubts European leaders show before admitting Kyiv into the Nato alliance will embolden Russia to attack more countries.
An option being weighed is major powers offering Ukraine bilateral security assurances in the years before it becomes a full Nato member.
Meanwhile, the British defence minister, Ben Wallace, has said that Britain supports adding Ukraine to the Nato and "that path is open" to them, although political realities may slow the process.
He added yesterday on the sidelines of the Shangri-La Dialogue security meetings in Singapore that it is not possible to add members in the middle of a war, and that the way forward is to continue aiding and arming Ukraine for both short- and long-term security.
"The best thing we can do to help Ukraine is now to help them defeat Russia," Wallace said in an interview. "After that is to make sure they're ready and capable and resilient."
Ukraine's membership of the Nato is on the agenda for the group's July summit in Vilnius, Lithuania.
Hanna Shelest, director of Ukrainian Prism, a think tank specialising in foreign policy and international security, said in Singapore that Nato membership would be a political decision.
"We are not expecting to see a strong decision (about Ukraine’s membership) at Vilnius," said Shelest, who is based in Ukraine. "But at a minimum we are hoping for a detailed roadmap."
Britain has, alongside other Western allies, provided Ukraine with billions of dollars' worth of assistance and weapons after Russia's invasion, which Moscow calls a "special operation".
Most recently, London supplied Storm Shadow cruise missiles, which Wallace said had been 100% successful in striking targets.
Security assurances for Ukraine are also in play, Wallace said, noting that such guarantees could range from mutual defence pacts to providing arms and ammunition.
There were few downsides to doing so, he added.
Wallace, whose has been mentioned as a possible successor to Nato Secretary-General Stoltenberg, said that he "wouldn't say no if he was offered it", but that it was up to members to decide.
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