The U.S. government has renewed its warning to Americans in Yemen they should leave the country in response to an "extremely high" security threat "due to terrorist activity and civil unrest."

"Terrorist organizations, including al Qaeda in the Arabian Peninsula (AQAP), continue to be active throughout Yemen. The U.S. government remains highly concerned about the possible attacks on U.S. citizens (whether visiting or residing in Yemen), and U.S. facilities, businesses, and perceived U.S. and Western interests," the travel warning says. "An ongoing risk of kidnapping exists throughout Yemen."

In addition to the terror threat, the State Department warning said, "Demonstrations continue to take place in various parts of the country and may quickly escalate and turn violent."

"U.S. citizens are urged to avoid areas of demonstrations, and to exercise extreme caution if within the vicinity of a demonstration," the warning says.

The State Department has been urging U.S. citizens to leave Yemen for months, with a similar travel advisory circulated in January.

A U.S. intelligence official declined to comment on the warning to ABC News, but one person briefed on intelligence in the region said the terror aspect of the warning could be related to perceived threats against Westerners at potential targets including shopping malls in Yemen and other Gulf nations.

Top U.S. officials have said that of al Qaeda's affiliates, AQAP is among the greatest threats to the U.S. homeland. One of its members, Ibrahim al-Asiri, is believed to be a master bomb maker, implicated in several bomb plots. Last week the State Department announced it had added a Norwegian-born bomb maker and member of AQAP to its designated terror list.

Last September another al Qaeda affiliate, al-Shabab based in Somalia, attacked neighboring Kenya's Westgate Mall, killing dozens.