Ankara has demanded Sweden prosecute those responsible for projecting a Kurdish flag onto Stockholm's parliament during Turkey's election.
Turkey has demanded action from Sweden after Kurdish groups inside the country staged a political stunt.
Video footage posted by the Rojava Committee, a Sweden-based group supporting armed Kurdish groups in Syria, showed a PKK flag being projected on the Swedish Parliament on the day of the Turkish president's re-election.
The PKK has fought an armed struggle for Kurdish autonomy and independence from the Turkish state since the 1980s. Ankara considers the group terrorists.
Turkey condemned the stunt on Tuesday, deploring what it called an "unacceptable" act at a time when Stockholm hopes to lift Turkey's veto on it joining NATO.
"It is completely unacceptable that PKK terrorists continue to act freely in Sweden, which is a candidate for NATO", said Fahrettin Altun, spokesperson for the Turkish presidency, on Twitter.
"We expect the Swedish authorities to investigate this incident and hold its perpetrators accountable," he added.
Ankara has blocked Sweden's NATO bid since May. It has been accused of using this leverage to extort political gains from Stockholm, which some claim would undermine Sweden's freedom of speech and sovereignty if it honoured their demands.
A Swedish parliament spokesperson said a number of people projected messages onto the building in Sweden's capital late on Sunday, adding it had no documentation about what was projected.
Call to release PKK founder
A call to release PKK founder Abdullah Öcalan was also screened by the Rovaja Committee, according to its protest video, which shows a burning effigy of the Turkish president.
A sworn enemy of the Turkish government, the PKK is classified as a terrorist organisation by Sweden, the European Union and United States.
The Turkish government has also asked Sweden to prevent a pro-Kurdish demonstration planned for Sunday in Stockholm, after a stricter anti-terrorism law is due to come into force on Thursday in the Nordic country.
Sweden dreaming of NATO
The incident took place after Erdogan won another five-year term in office, following presidential elections on Sunday.
He now has the mandate to carry on his muscular foreign policy, having objected to both Sweden's and Finland's bids to join NATO last year in the face of Russia's invasion of Ukraine.
Turkey ratified Finland's bid in March and obtained, belatedly, a Turkish green light and officially entered NATO on 4 April.
But Erdogan still objects to Sweden, saying Stockholm harbours members of the PKK and that it has not fulfilled its part of last year's deal meant to assuage Ankara's security concerns.
Some of those the Turkish president wants extradited are political opponents, such as exiled journalist Bülent Keneş, who have criticised him in the past.
Although bids for membership must be approved by all members, NATO chief Jens Stoltenberg said he was "totally serene" on Tuesday in Oslo about Sweden joining the Atlantic Alliance, despite the re-election of Erdogan.
Sweden has another stone in its shoe: Hungary.
Budapest also has yet to ratify its NATO bid and is demanding Stockholm ceases to accuse it of backsliding on matters related to the rule of law.