Turkish police said they had not found evidence of any concrete threat to foreigners after detaining 15 Islamic State suspects accused of targeting consulates and non-Muslim houses of worship, state media reported on Sunday.

Last week, several European consulates in Istanbul were shut citing “security reasons” and several Western states warned citizens of a heightened risk of attacks to diplomatic missions and non-Muslim places of worship in Turkey, following a series of far-right Koran-burning protests in Europe in recent weeks.

State-run Anadolu Agency cited an Istanbul police statement saying the 15 suspects had “received instructions for acts targeting consulates of Sweden and the Netherlands, as well as Christian and Jewish places of worship”.

While the suspects’ ties to the jihadist group were confirmed, no concrete threats toward foreigners were found, the statement said.

Ankara summoned nine ambassadors to criticise the coordinated closure of the European consulates and Turkish officials later said the Western nations had not shared information to back up their claims of a security threat.

Turkey suspended negotiations for Sweden and Finland’s NATO accession following a protest in Stockholm during which a copy of the Muslim holy book, the Koran, was burned.

Foreign Minister Mevlut Cavusoglu repeated on Saturday Turkey’s frustration with what it says is Sweden’s inaction toward entities Ankara accuses of terrorist activity.

Turkey, Sweden and Finland signed an agreement in June last year aimed at overcoming Ankara’s objections to their NATO bids, with the Nordic states pledging to take a harder line primarily against local members of the banned Kurdistan Workers Party (PKK).