Sweden's foreign minister said on Thursday he was no longer sure his country would be able to join NATO by July, after fresh signs of objections from Hungary.
Sweden applied to join the military alliance after Russia's invasion of Ukraine last year, but Hungary and fellow NATO member Turkey held off from approving the bid.
Foreign Minister Tobias Billstrom said last week that "it goes without saying" Sweden would become a member by the time of a NATO summit in Vilnius in July.
But he told TT news agency on Thursday: I have noted the things that have been said in recent days, especially from Hungary's side, and that means you always have reason to alter your words.
"I think 'hopeful' in this context is better," he added.
A day earlier, a Hungarian government spokesperson said it was holding up Sweden's admission because of "grievances" over Stockholm's past criticism of Prime Minister Viktor Orban's policies.
Turkey has accused Sweden of harbouring members of the Kurdistan Workers Party (PKK), considered a terrorist group by Ankara and its Western allies.
Relations were worsened by a protest in January near the Turkish embassy in Stockholm at which a far-right politician burned a copy of the Muslim holy book, the Quran.
Sweden's government has said it takes Turkey's allegations seriously but added there are some demands, such as extraditing people that Turkey deems harmful, that it cannot meet.
Finland applied to join NATO at the same time as Sweden. Its NATO membership was approved by the Hungarian parliament on Monday and is expected to be ratified by Turkey soon.