The detentions come after the British embassy in the capital Ankara was closed today because of security concerns, the UK Foreign Office said, and after the German embassy said its missions in Turkey were providing "limited services until Friday".
Three people in the capital Ankara and one person in Istanbul were detained before the Muslim Eid al-Adha holiday on Monday, but interior ministry officials said there was no evidence linking the suspects to terrorist organisations, Anadolu news agency reported.
The British embassy, closed for consular services this week, had been due to reopen on Friday after the Islamic holiday began on Monday.
In the last 12 months, Turkey has been hit by a series of attacks blamed on IS extremists and Kurdish militants. Foreign missions have closed down on occasion due to security alerts.
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Richard Moore, British ambassador to Turkey, said on Twitter that it was a "precaution" to close the embassy.
He added that British officials were "working closely and cooperatively with Turkish authorities".
Mass-circulation German daily Bild had said that German missions and German schools in Turkey were closed due to fears of an attack.