Highlighting the "recent terrorist attacks" in Saudi Arabia and Turkey, the US State Department has issued a worldwide warning that the Al Qaeda network may stage new attacks, designed to be more "devastating" than the September 11 strikes.

In a "worldwide caution" against attacks and plane hijackings, the State Department has warned that "US citizens may be a target of terrorist actions."

Deeply concerned about the security of American citizens overseas, the alert, issued on Friday, cautioned them to "maintain a high level of vigilance, to remain alert and to take appropriate steps to increase" their security awareness.

"We are seeing increasing indications that Al Qaeda is preparing to strike US interests abroad," said the warning, which came a day after 27 people were killed and more than 450 injured in two bomb attacks on British targets in Istanbul.

"The Al Qaeda and its associated organisations have struck in the Middle East in Riyadh, Saudi Arabia, and in Europe in Istanbul, Turkey. We therefore assess that other geographic locations could be venues for the next round of attacks," it said.

"We expect Al Qaeda will strive for new attacks designed to be more devastating than the September 11 attack, possibly involving non-conventional weapons such as chemical or biological agents. We also cannot rule out that Al Qaeda will attempt a second catastrophic attack within the US," the alert said.

"Terrorist actions may include, but are not limited to, suicide operations, hijackings, bombings or kidnappings. These may also involve commercial aircraft and maritime interests, and threats to include conventional weapons, such as explosive devices," the alert said.
  
Since terrorists do not distinguish between official  and civilian targets, they might strike at facilities where US citizens and other foreigners congregate or visit, including residential areas, clubs, restaurants, places of worship, schools, hotels, outdoor recreation events or resorts and beaches, the alert said.