U.S. citizens citizens in Yemen were urged to leave immediately because terror activities pose a \"high security threat,\" the State Department said Tuesday. The State Department also ordered non-emergency U.S. government personnel evacuated from Yemen \"due to the continued potential for terrorist attacks.\" \"The U.S. Department of State warns U.S. citizens of the high security threat level in Yemen due to terrorist activities and civil unrest,\" the department\'s travel warning said. \"U.S. citizens currently in Yemen should depart.\" Last week, the State Department issued a worldwide travel alert for U.S. citizens and closed nearly two dozen embassies because it determined there was a credible threat of terrorism against an unknown target. Because of lower staffing levels, the U.S. Embassy in Sanaa may be limited to assist Americans in an emergency and provide routine consular services, the warning said. \"The security threat level in Yemen is extremely high,\" the warning read. \"Terrorist organizations, including al-Qaida in the Arabian Peninsula [AQAP], continue to be active throughout Yemen. The U.S. government remains highly concerned about possible attacks on U.S. citizens [whether visiting or residing in Yemen], and U.S. facilities, businesses, and perceived U.S. and Western interests.\" U.S. citizens remaining in Yemen despite the travel warning were told to limit non-essential travel within the country and make their own contingency emergency plans. Those wishing to leave Yemen should make plans to leave as quickly as possible, the warning said. The airport was open and commercial flights were operating. The State Department said there were no current plans for U.S. government-sponsored evacuations. In Washington Monday, White House spokesman Jay Carney said an alert that forced U.S. embassy closures across the Middle East and Africa may remain in place all month. \"Our current information suggests that al-Qaida and affiliated organizations continue to plan terrorist attacks both in the region and beyond,\" Carney said during a media briefing. \"And our information suggests that they may focus efforts to conduct attacks in the period between now and the end of August,\" he said. The administration\'s decision last week to close the diplomatic missions and issue a worldwide travel alert came after U.S. counter-terrorism officials intercepted electronic communications in which al-Qaida leader Ayman al-Zawahiri -- who succeeded Osama bin Laden -- ordered the head of the terrorist group\'s Yemeni affiliate to carry out an attack as early as Sunday, U.S. officials told several news organizations. \"The threat is emanating from and may be directed toward the Arabian Peninsula, but it is beyond that, potentially,\" Carney said. \"And that is why we have taken some of the actions we\'ve taken.\" Nineteen embassies and consulates -- including in Yemen, Libya, Egypt, Saudi Arabia and the United Arab Emirates -- will remain closed through at least Saturday, the State Department said. Embassies in Afghanistan, Algeria and Iraq reopened Monday after Sunday\'s one-day closure. \"We are going to keep evaluating information as it comes in, keep analyzing the various intelligence that we\'re getting in in regards to this stream,\" State Department spokeswoman Marie Harf said Monday. \"I don\'t want people to think that we\'re leaning toward indefinite closure of these facilities -- we\'re focused on this week,\" she said. Carney and Harf declined to link the terror threat to the National Security Agency\'s leaked electronic surveillance activities and programs.