The U.S. says it has received warnings of possible plans to kidnap its citizens in the Gaza Strip.
American citizens are being warned to defer travel plans to Israel, the West Bank and Gaza Strip.
The U.S. Embassy in Tel Aviv issued the alert after receiving what it called credible reports of plots to kidnap U.S. citizens in Gaza.
Gaza is a stronghold of Hamas and the Islamic Jihad, two groups that carry out suicide bombings and other attacks. Both organizations have been listed as terrorist groups by the State Department.
Hamas and Islamic Jihad strongly opposed the recent U.S.-led war in Iraq. The organizations have also denounced the U.S. backed "road map" to peace which calls for the establishment of a Palestinian state in peaceful coexistence with Israel.
"At this time, Americans are advised to be particularly cautious," said a security alert on the web site of the U.S. Embassy in Tel Aviv.
The warning also said that American tourists, students and residents had been affected by a recent spate of attacks in the region and that the potential was strong for a new wave of terrorism.
Americans are being urged to remain in close contact with the U.S. Embassy in Tel Aviv and the American Consulate in Jerusalem and should consider "relocating to a safe location", the security alert advises.
U.S. citizens are also being told to avoid public places such as restaurants, cafes, shopping areas, pedestrian malls, public buses and crowded venues, all of which are potential targets of suicide bombings.
In addition, the advisory said U.S. Embassy and Consulate personnel are barred from using public buses throughout Israel, the Jerusalem municipality, the West Bank and Gaza.