Turkish prosecutors are investigating an "incident" in Stockholm involving a suspended effigy of President Tayyip Erdogan, Reuters reports.

The footage, first posted on Twitter by the Swedish Solidarity Committee in Rustavi, shows an effigy of Erdogan suspended at his feet outside Stockholm City Hall, with several people standing next to him.

Swedish Prime Minister Ulf Kristersson told TV4 on Friday that the act was extremely serious and he considered it sabotage against the country's bid for NATO membership. The police said they knew nothing about the incident.

Turkey summoned the Swedish ambassador in connection with the incident.

Turkey's state-run Anadolu news agency reported that the investigation was launched after Erdogan's lawyer filed a lawsuit. 

Echoing pro-government Turkish media that broadcast footage of the incident, Aydın noted that the incident is believed to have been organized by the Kurdistan Workers' Party (PKK).

Last year, Sweden and Finland signed a trilateral agreement with Turkey aimed at overcoming Ankara's objections to their NATO membership applications, which require the approval of all 30 NATO member states.

A diplomatic source said Turkey conveyed its reaction to Swedish Ambassador Staffan Herrström at the Foreign Ministry. Stockholm confirmed that he had been summoned.