A security source on Saturday reported that the Iranian activity in Istanbul, Turkey, against Israelis has already begun and that it was a "very serious incident that is hard to lay hands on."

The source said that several attempts to carry out an attack in Istanbul had already been foiled, but clarified that the Iranian cells on the ground know about the Israelis who are at hotels in the city.

"I call on all the Israelis who are in Turkey right now to obey instructions from security sources," Defense Minister Benny Gantz (Blue and White) said Saturday. "Israel is acting to foil the Iranian attempts to carry out terror attacks, and is preparing to respond with force to any attacks on Israeli citizens - in any location."

Kan News quoted a security source as saying, "The incident is not behind us; there are still immediate attempts by cells to murder Israelis on the ground. There are Israeli families who were a minute from death, and we warned them as well, and we can say that the Israelis lowered their profile."

The sources added that there are great efforts by Israeli security forces, including the Mossad, to foil the terror attack. According to them, "the cooperation between the Israeli forces and the Turks is unusual, and really shoulder-to-shoulder, and it is starting to bear fruit."

Senior Israeli security sources reiterated that there are real warnings of a terror attack in the Turkish city, and that Israelis who are currently in Istanbul should leave the city. Those who cannot leave are asked to limit their activities as much as possible, close themselves in their rooms, and hide signs that they are Israeli.