Three U.S. military officials stressed strongly that the scenario is very unlikely.

"No one has even drawn an evacuation plan on the back of a cocktail napkin yet," one official said. But the three ships have been told to stay in place until there is more certainty about what is happening.

The U.S. Embassy in Tel Aviv took precautionary measures Friday, reducing its staff and suspending routine consular services, according to an embassy security message. Additionally, embassy staff were instructed to keep their children home from school for the day and were prohibited from traveling to the south of Israel.