According to the Counter-Terrorism Bureau, it has identified potential threats against Israeli targets mainly in, although not restricted to, the Middle East and Africa.
The warnings come ahead of the Jewish religious and national holidays of Passover, Independence Day, Shavuot and Lag B'Omer, all of which take place between April-June.
"It should be noted that there are no new travel warnings except that of Turkey, which was revised recently," a statement released by the Counter-Terrorism Bureau noted.
It went on to reference the deadly March 19 attack carried out by ISIS in Istanbul in which three Israeli tourists were killed in a terrorist bombing as evidence of the "high capabilities of carrying out further attacks."
"Terrorist infrastructures in Turkey continue to advance additional attacks against targets – including Israeli tourists – throughout the country," the statement added.
The assessment concluded that in the wake of the threats identified, the existing travel warning vis-à-vis Turkey had been upgraded from a basic concrete threat to a high concrete threat reiterating "our recommendation to the public to avoid visiting the country and – for Israeli currently in Turkey – to leave as soon as possible."
The Counter-Terrorism Bureau also urged Israelis located in the countries highlighted to remain alert particularly during the approaching Jewish holidays.
Moreover, the warning lists a variety of potential targets including "popular tourist spots, sports stadiums, cultural sites, shopping centers, hotels, airports and public transport" while travelers were called upon to "exercise due caution at all times; groups are urged to avoid drawing attention to themselves (by manner of dress, language and other identifying signs)."
Additionally, the warning cautions against accepting "tempting and unexpected business or social offers, especially in isolated areas and during the late hours."
It also advised that Israelis keep an irregular routine such as changing regular journey routes, restaurants, entertainment sites and hotels.
A Counter-Terrorism Bureau official commented that "We recommend to avoid visiting Turkey and to leave the country immediately, particularly its major cities and holiday resorts, in light of the increased severity of the week's security warnings. The present danger posed against all Israelis and westerners exists throughout the whole of Turkey."
Despite the warning however, the official added that while Israelis should remain cautious and alert in crowded areas and are advised to avoid such areas, "there are no warnings for Israelis in Western Europe."
"There is no connection whatsoever between the warnings and the diplomatic situation. We will heighten or lessen the warning level," the official added.
"Anyone who has booked a holiday to Turkey - and we received hundreds of calls - we recommend them to cancel their holidays and change their destination. We have contacted travel agencies and requested that they enable prospective travelers to cancel and rearrange their tickets without incurring additional fees."
In addition to the threat posed by ISIS, the Counter-Terrorism Bureau also warned of potential terrorist activities by Boko Haram and Al-Shabab in Nigeria, Cameroon, Chad and Nigeria and global Jihad organizations in Tunisia.
The warning further noted a "world terror campaign" launched by Hezbollah and Iran which, it said, "constitutes a continuing threat against Israelis and Jews throughout the world," and listed the countries from which Israelis are forbidden to visit such as Syria, Iraq, iran, Lebanon, Yemen and Saudi Arabia.
Very high concrete threats regarding travel to: Afghanistan, Libya, Sudan and Somalia.
High concrete threats regarding travel to: Algeria, Djibouti, Mauritania, Tunisia, Burkina-Faso, Indonesia, Ivory Coast, Malaysia, Mali, Pakistan, Niger, Turkey and Togo.
Basic concrete threats regarding travel to: Bahrain, Egypt Jordan, Kuwait, Qatar and the United Arab Emirates.
Continuing potential threats regarding travel to: Azerbaijan, Morocco, Oman, Kenya and Nigeria.