Turkey summoned Denmark's ambassador on Friday to condemn Copenhagen for allowing a far-right extremist to burn Korans over Ankara's refusal to let Sweden and Finland join NATO.

Anti-Islam activist Rasmus Paludan, a Danish-Swedish dual national, first burnt a copy of the Muslim holy book near a mosque in the Danish capital and then a second copy outside the Turkish embassy.

A decision by Swedish police to allow Paludan to stage a similar protest in Stockholm prompted Turkey to postpone planned NATO accession talks with Sweden and Finland.

The US and French embassies in Ankara warned their citizens of an increased risk of reprisal attacks in Turkey.

"In the wake of recent Quran-burning incidents in Europe, the US government cautions its citizens of possible retaliatory attacks by terrorists against places of worship in Turkey," said the US embassy.

"Terrorists could attack with little or no warning, targeting places of worship or places Westerners frequent," the embassy added, urging people to stay alert and avoid crowds.

The French embassy sent an email telling its citizens in Turkey to be "highly vigilant" and underlined the US warnings.

A Turkish diplomatic source said the Danish ambassador was summoned to protest at his country's "unacceptable" attitude towards Paludan's actions.

"We strongly condemn the decision to grant permission for this provocative act, which clearly constitutes a hate crime," the Turkish diplomatic source told reporters.

- 'Open democracy' -

Danish Foreign Minister Lars Lokke Rasmussen confirmed the envoy had been summoned. He said Copenhagen enjoyed "good relations with Ankara -- and this doesn't change that".

RTL

Anti-Islam activist Rasmus Paludan is notorious for his provocative stunts / © AFP

"Our job is to explain to Turkey the conditions that prevail in Denmark with our open democracy, and make them understand that there is a difference between Denmark as a country -- our people as a whole -- and individuals who hold a wide range of views," he said.

Paludan vowed on Friday to stage weekly actions involving the Koran until Turkey approves Sweden and Finland's NATO membership.

Swedish leaders have strongly condemned Paludan's action but defended their country's broad acceptance of free speech.

Last year, Finland and Sweden broke with decades of military non-alignment and applied to join NATO in response to Russia's invasion of Ukraine.

Bids to join NATO must be approved by all 30 members of the alliance.

Turkey and fellow NATO member Hungary are the only members that have yet to ratify the two applications by votes in parliament.

Hungary's parliament is expected to ratify the two bids next month.