After Russia invaded Ukraine, Sweden and Finland tore up their long-standing policies of military non-alignment and asked to join the US-led military alliance.

The move has strong backing from most NATO members.

But Turkish President Recep Tayyip Erdogan has objected, accusing the Nordic neighbours of harbouring Kurdish militants hostile to Ankara, especially supporters of the outlawed Kurdistan Workers' Party (PKK).

"We will be able to fulfil the memorandum and its items. I'm quite sure of that," Billstrom said of an agreement Sweden and Finland signed with Turkey in June designed to iron out the concerns.

Billstrom told AFP in an interview that Sweden backed the stance Turkey and the European Union have taken on the PKK.

He said the group was "terrorist through and through" and Sweden respected Turkey's security concerns.

But the new top diplomat, who took office last week, also stressed, "It's necessary to have a balance of freedom of expression."

Kurdish groups in Sweden staged several demonstrations during the summer and waved PKK flags, which raised hackles in Turkey.

Under the deal with Turkey, Sweden and Finland have agreed to address Ankara's requests for "terror suspects" to be deported or extradited.

- 'In a legally safe way' -

Billstrom said Stockholm would deliver on promises made but stressed this had to be done in "a legally safe way ... in line with the constitution".

In Sweden, if a suspect opposes his or her extradition, the objection must be examined by the Supreme Court, which can effectively block the government from granting the warrant.

In August, Stockholm authorised the first extradition to Turkey since the Madrid accord was reached but that case concerned fraud and not terrorism.

In late September, Swedish authorities lifted a ban on military exports to Turkey, another of Ankara's demands.

Billstrom stressed there was "positive dialogue with Turkey", noting that he and new Prime Minister Ulf Kristersson would be visiting Ankara shortly.

Although Turkish officials have said their main concerns relate more to Sweden than Finland, Billstrom said he did not expect Helsinki to go ahead and join NATO without its neighbour.

"No, we don't see any signs in that direction," he said.