Israeli travelers in Turkey were urged this week to lay low and return home as soon as possible amid concerns they would be targeted in an Iranian revenge attack.

Some 100 Israelis in Turkey received mobile text messages from security officials with the warning. After news of the warning broke, hundreds of Israelis cancelled travel plans to Turkey.

Former National Security Council head Maj. Gen. (ret.) Giora Eiland said on Tuesday that this was more than just a precautionary step. Such a warning would only be issued if an Iranian death squad was already on the ground and hunting its targets, he surmised in remarks to Ynet.

The feared Iranian attack is believed to be in response to the killing of Islamic Revolutionary Guard Corps’ Col. Hassan Sayyad Khodaei on May 22 in Tehran. Israel is widely believed to be behind the hit.

See: Israel’s Long Arm Reaches Revolutionary Guards in Iran

Speaking to Ynet news, Eiland said: “The immediacy of the warning and its tone shows that it is based on concrete information regarding not only an intent but the ability to carry out an attack. In other words, Israeli intelligence either knows or estimates that an Iranian squad is already in Turkey to launch an attack against Israelis.”

He said that based on his experience, the decision to issue such a significant travel advisory also has economic and international diplomatic consequences.

With reporting by JNS.