A memorandum signed by the three nations follows talks between their leaders at a NATO summit in Madrid and ends what appeared to be the key obstruction to the Nordic neighbours' accession process.

A statement from Finnish President Sauli Niinisto said: "We had a thorough meeting with president of Turkey Recep Tayyip Erdogan and prime minister of Sweden Magdalena Andersson, facilitated by secretary general of NATO Jens Stoltenberg.

"As a result of that meeting, our foreign ministers signed a trilateral memorandum which confirms that Turkey will at the Madrid summit this week support the invitation of Finland and Sweden to become members of NATO."

Mr Stoltenberg said Russian President Vladimir Putin would now be "getting more NATO on his borders".

"I am pleased to announce that we now have an agreement that paves the way for Finland and Sweden to join NATO," he said.

"Turkey, Finland and Sweden have signed a memorandum that addresses Turkey's concerns, including around arms exports and the fight against terrorism."

Finland and Sweden will receive a formal invitation to join the organisation on Wednesday, which will then require further steps like domestic ratification.

The Nordic states' attempt to join the alliance hit a stumbling block when President Erdogan said they supported Kurdish militants.

In the memorandum, Finland and Sweden stated they would not support the YPG/PYD, and the group known in Turkey as FETO.

The Nordic states also stated that they deemed the PKK "a proscribed terrorist organisation".

The statement from Finland said: "Our joint memorandum underscores the commitment of Finland, Sweden and Turkey to extend their full support against threats to each other's security. Us becoming NATO allies will further strengthen this commitment.

"Over the past weeks, Turkey has raised its concerns over the threat of terrorism. Finland has constantly taken these concerns seriously.

"Finland condemns terrorism in all its forms and manifestations. As a NATO member, Finland will commit fully to the counterterrorism documents and policies of NATO."

The traditionally neutral nations decided to apply for NATO membership following the Russian invasion of Ukraine.

In response to Tuesday's announcement, Prime Minister Boris Johnson said: "Fantastic news as we kick off the NATO summit.

"Sweden and Finland's membership will make our brilliant alliance stronger and safer."