Reports that terrorists from the so-called Islamic State have advanced plans to murder Jewish children in Turkey, targeting kindergartens and schools and youth centres.
Information on what intelligence officials are describing as "an imminent" attack was obtained from six operatives from the "Caliphate" who were arrested in the southern city of Gaziantep over the last week.
The most likely target of an attack is Istanbul's synagogue in Beyoglu which also has a community centre and a school attached to it.
"In light of these circumstances, extraordinary security measures are being taken above and beyond the high alert level already in place by the Turkish police, as well as vigilance within the Jewish community," an intelligence source told Sky News.
"Undercover and other covert counter-terror measures are being implemented around the clock.
"This is a more than credible threat. This is an active plot," the source added.
The series of threats and the specific targeting of Jewish children follow the deadly attack in Istanbul on 19 March when five people were killed by a suicide bomber, including four Israelis, and the murder of another 35 in Brussels last week.
The latest intelligence has emerged as spy agencies struggle to co-ordinate their response to the scale of the threat that is now perceived to exist across Europe.
