Turkey has summoned Sweden's ambassador to Ankara to protest against "insulting" images of President Recep Tayyip Erdogan.
Kurdish "propaganda" -- featuring Erdogan's face -- was allegedly projected onto the Turkish Embassy building in Stockholm.
The protest was reportedly held by supporters of the Kurdistan Workers Party (PKK), which Turkey and the European Union both consider a terrorist organisation.
Turkey's foreign ministry condemned the images and has called for an investigation, according to the state-run Anadolu Agency.
Swedish ambassador Staffan Herrstrom was also summoned to the ministry on Monday, the agency added.
The incident comes at a sensitive time in bilateral relations, as Sweden and Finland are seeking Turkey's approval of their bid to join NATO.
The two Nordic countries abandoned their longstanding policies of military nonalignment this year after Russia invaded Ukraine in February.
But NATO-member Turkey has not yet endorsed their accession, which requires unanimous approval from existing alliance members.
Ankara has repeatedly called on Sweden to take “concrete steps” against groups that Turkey considers to be security threats.
Erdogan’s government is pressing the two countries to crack down on supporters of the outlawed PKK, as well as those suspected of orchestrating a failed 2016 coup in Turkey.
Earlier this month, Sweden’s prime minister Ulf Kristersson visited Turkey and pledged to work toward countering “terrorism” threats to Turkey.
The summoning of the ambassador also comes as Turkey threatens to launch a ground offensive against Kurdish militants in Syria.
At least two people were killed in suspected strikes in the Turkish border town of Karkamis on Monday.