The announcement was a crucial step towards unblocking Sweden's bid to join the alliance, after resistance from Orban's nationalist government which accused Swedish officials of being hostile to it over rule-of-law issues.

Budapest has a fleet of 14 Jas-39 Gripen fighter jets it operates under a leasing contract signed in 2001, which has since been extended twice.

"Today, we have reached an agreement to add four aircraft to the Hungarian Defence Forces' Gripen fleet," Orban said after talks with Swedish Prime Minister Ulf Kristersson.

"On Monday, the Hungarian parliament will meet and take the necessary decisions, and with this we have closed one phase and opened a new one," he added.

Kristersson arrived in the Hungarian capital earlier on Friday, just three days ahead of a vote by Hungary's parliament on the Nordic country's bid to join NATO.

Hungary remains the last obstacle to Stockholm's NATO membership after Turkey's ratification last month.

Following Russia's invasion of Ukraine, Sweden alongside neighbouring Finland applied to join NATO in May 2022.

"The conversation has been constructive and we have agreed to move forward in fields of common interests," Kristersson said at a press conference after talks with Orban.

"We do not agree on everything, but we do agree that we should work more actively together when we have common ground," he added.

Earlier on Friday, Orban told state radio that "some pending (bilateral) military and arms issues" had to be worked out before the Hungarian parliament on Monday "can put the final seal" on ratification.

"We are pro-peace, and the Swedes are pro-war in the Russian-Ukrainian conflict," Orban said, but added that the "clear differences in values" could be bridged.

- 'On course' -

Faced with increasing pressure from the United States and fellow EU member states to greenlight Sweden's NATO bid, Orban announced last week that Budapest was "on course" to ratify it.

His nationalist Fidesz party -- whose ruling coalition with the Christian democratic KDNP holds a majority in parliament -- indicated it would support Sweden's bid on Monday.

All opposition parties except the far-right Our Homeland movement are in favour of ratification.

Although Hungary repeatedly said it supports Stockholm in principle, it prolonged the process by asking Sweden to stop "vilifying" Orban's government.

It has often denounced what it called Sweden's "openly hostile attitude", accusing Swedish representatives of being "keen to bash Hungary" on rule-of-law issues.

In January, Orban invited the Swedish prime minister to Hungary, citing the need to "build strong mutual trust" through "more intense political dialogue".

Finland became the 31st member of NATO in April 2023.