The Turkish Foreign Ministry called the Swedish ambassador to the carpet over images "insulting" President Recep Tayyip Erdogan.

Images of Erdogan and Kurdish rebels were projected on the Turkish embassy in Stockholm.

Ambassador Staffan Herrstrom was summoned to the Turkish Foreign Ministry, where officials condemned the incident, called for an investigation and again demanded that Stockholm take "concrete steps" against groups that Turkey considers a security threat.

Sweden and Finland applied for NATO membership this year. But Turkey, a NATO member, has yet to approve their entry, which requires unanimous approval of existing members of the alliance.

Erdogan's government is pressuring the two countries to crack down on individuals it considers "terrorists," including supporters of the Kurdistan Workers' Party and Islamic preacher Fethullah Gulen's movement, whom Ankara accuses of masterminding the failed 2016 coup in Turkey.

Earlier this month, Sweden's new prime minister, Ulf Kristersson, visited Turkey and pledged to work to counter "terrorist" threats to Turkey.