Hungary's ratification is the last obstacle to the Nordic country's membership which Stockholm sought after the Ukraine conflict began.

"It's unacceptable, not only from my point of view, that one country can block the other one, especially in the context of the war with Russia in Ukraine," Tusk told reporters as he hosted his Swedish counterpart Ulf Kristersson in Warsaw.

Although it supports Stockholm in principle, Budapest prolonged the process by asking Sweden to stop "vilifying" the Hungarian government, which is accused by critics of being authoritarian.

However on Saturday, Hungarian Prime Minister Viktor Orban said he and the Swedish premier had "taken important steps in order to rebuild trust".

Orban also said the "dispute with Sweden is moving towards a conclusion" and that Hungary was "on course" to ratify the bid..

Asked about the remarks, Kristersson said Monday that Orban was better suited to answer that question.

"I don't know specifically what he meant by that... I simply think there is a strong will to finalise this process of NATO accession," Kristersson said.

Swedish authorities have repeatedly refused to hold talks with Hungary on the ratification despite Orban inviting his Swedish counterpart to "negotiate" NATO accession.

After Russia's invasion of Ukraine, Sweden announced its application to join NATO in May 2022, at the same time as Finland, which became the organisation's 31st member in April..