"Neither of these countries have a clear, open attitude towards terrorist organisation. How can we trust them?" the Turkish president said.

Turkey accuses the two Nordic nations of harbouring members of the Kurdistan Workers' Party (PKK), a group it views as a terrorist organisation, and followers of Fethullah Gulen, who Ankara accuses of orchestrating a 2016 coup attempt.

Mr Erdogan's government has also pledged to block applications from countries that have imposed sanctions on it.

In 2019, both Nordic nations slapped an arms embargo on Ankara after its incursion into Syria.

Sweden has formally announced its decision to join Nato, a move that will end the Scandinavian country's centuries-long military non-alignment.

"Nato will strengthen Sweden, Sweden will strengthen Nato," Ms Andersson said at a briefing in Stockholm on Monday.

She said Europe was now living in a dangerous new reality, referring to Russia's invasion of Ukraine.

Last week, Sweden's neighbour Finland said it would seek Nato membership. Russia criticised both announcements.

"We are leaving one era behind us and entering a new one," Prime Minister Magdalena Andersson told lawmakers in Stockholm on Monday.

She said a formal application could be handed within several days and would be synchronised with Finland. Nato has signalled its willingness to admit the two new members.

However, Ms Andersson stressed that Sweden did not want permanent Nato bases or nuclear weapons on its territory.

Norway, Denmark and Iceland - all Nato members - immediately said they were ready to support Sweden and Finland by all means necessary if they came under attack.

The UK, also a Nato member, has already given security guarantees to Sweden and Finland to cover the transition period.

Monday's announcement by Sweden came as Nato began one of its biggest exercises in the Baltic region, involving some 15,000 troops. Named "Hedgehog", the drills in Estonia involve 10 countries, including Finland and Sweden.

BBC