The U.S. State Department says it is "deeply concerned" about the security of U.S. citizens overseas, adding that there are indications the al-Qaida terrorist network is preparing to strike U.S. interests abroad.

The statement cautioned U.S. citizens to maintain a high level of vigilance, to remain alert, and to take appropriate steps to increase their security awareness.

The State Department noted most recent attacks by "al-Qaida and its associated organizations" have been in the Middle East and Europe. But it said attacks also could take place in other regions, and it said the government "cannot rule out" attempts at what it called a "catastrophic attack" within the United States.

U.S. government facilities worldwide remain at a heightened state of alert. The statement said attacks could occur at places civilians congregate or visit, such as residential areas, clubs, restaurants, places of worship, hotels, and public areas.