"We are going to ensure that all those present on Sunday are able to exercise their rights protected by the constitution", including freedom of expression, Stockholm police spokesman Ola Osterling said.

The demonstration, which is scheduled to take place on Sunday in the city centre, is titled "No to NATO, No Erdogan Laws in Sweden".

It is organised by the "Alliance against NATO", which includes the pro-Kurdish Rojava Committee among others.

Erdogan, re-elected for five more years on May 28, has so far blocked Sweden's NATO membership, accusing Stockholm of being a haven for Kurdish activists Turkey considers "terrorists".

He has demanded that Stockholm extradite several dozen activists, though those decisions can only be made by Sweden's independent judiciary.

Earlier this week, Ankara expressed its frustration over the planned demonstration, organised by groups close to the Kurdistan Workers' Party (PKK) which is outlawed by Turkey.

Even though the PKK is also considered a terrorist organisation in Sweden -- as in the rest of the EU -- its supporters are generally allowed to protest in public.

A spokesman for the Turkish presidency on Tuesday said it was "completely unacceptable that PKK terrorists continue to operate freely in Sweden" and urged Swedish authorities to block them from demonstrating on Sunday.

A new law beefing up Sweden's anti-terror efforts came into effect on June 1, criminalising "participation in a terrorist organisation".

But the new law is not aimed at attacking freedom of speech, Sweden's justice minister reiterated on Friday.

Asked about the possible presence of PKK activists at Sunday's demonstration, the police spokesman said they were "also protected by the constitution."

"This demonstration will go very well, that's how we see the situation," Osterling said.

Turkey and Hungary are the only two NATO countries yet to ratify Sweden's membership bid.

NATO chief Jens Stoltenberg will visit Turkey at the weekend to attend Erdogan's inauguration and try to lift the final obstacles.