Sweden's defence ministry said that the two nations were negotiating a deal for "even closer cooperation with the United States both bilaterally and within the framework of NATO".

Exactly what the so-called Defence Cooperation Agreement (DCA) will cover is being negotiated "but it makes it easier for American troops to operate in Sweden," Defence Minister Pal Jonson said in a written statement to AFP.

"It could entail storage of military supplies, investments in infrastructure to enable support and the legal status of American troops in Sweden," Jonson said.

"The negotiations are started because Sweden is on its way of becoming an ally of the United States, through the NATO membership," the minister added.

Sweden and Finland broke with decades of military non-alignment and applied to join the US-led defence alliance last year in response to Russia's February invasion of Ukraine.

Turkey has refused to ratify their NATO applications, accusing both countries of providing a safe haven for outlawed Kurdish groups it deems "terrorists".

Most of Turkey's demands have involved Sweden because of its more robust ties with the Kurdish diaspora.

Ankara has notably demanded that Sweden extradite people Turkey accuses of terrorism or of having played a part in the 2016 attempt to topple President Recep Tayyip Erdogan.

During a security conference in Sweden on Sunday, Swedish Prime Minister Ulf Kristersson, who met with Erdogan in Turkey in December, said some of Ankara's demands could not be accepted by Sweden.

"Turkey has confirmed that we have done what we said we would do, but it also says that it wants things that we can't, that we don't want to, give it," Kristersson said.