WASHINGTON (CNN) -- The State Department has issued a public announcement regarding the situation in Yemen, warning U.S. citizens to defer non-essential travel following the shooting deaths Tuesday of four kidnapped tourists.

Three Britons and an Australian were killed when Yemeni security officials stormed a hideout where the extremist Islamic Jihad held 16 hostages, including Americans.

U.S. citizens in Yemen are advised to exercise a high level of vigilance, to avoid travel outside major cities and to contact the U.S. Embassy in Sanaa by telephone or fax for up-to-date information on security conditions.

The announcement follows a December 24 Worldwide Caution in which the State Department urges all American citizens traveling or residing abroad to remain vigilant with regard to their personal security practices.