The State Department warned Americans overseas Thursday to stay vigilant because of "the continuing threat of terrorist actions" against U.S. interests worldwide, including possible suicide attacks aimed at U.S. civilians.

The government "continues to receive credible indications that extremist groups and individuals are planning additional terrorist actions against U.S. interests," the department said in a global alert.

"American citizens may be targeted for kidnapping or assassination," warned the department.

The alert comes a day after the FBI issued a similar alert to state and local authorities across the country.

Both alerts cited as a reason for concern a recently released taped statement attributed to Usama bin Laden and separate information obtained from Al Qaeda detainees indicating possible attacks against U.S. targets.

Still, the official color-coded national terrorist alert level remains at code yellow -- "significant risk" -- because officials do not have any specific information detailing where and when an attack might occur. Yellow is the third-highest of five threat levels.

Meanwhile, authorities in New York increased security Thursday at the city's landmark buildings, bridges, financial centers and tourist attractions in response to the FBI warning.

Harbor patrols kept a closer watch on bridges linking Manhattan to the city's other boroughs, police said. Tunnels were also under closer scrutiny, and police presence was increased throughout lower Manhattan where the World Trade Center once stood.

In an audio taped message that aired Sunday on the Arab satellite TV station al-Jazeera, a voice believed to be that of bin Laden refers to Al Qaeda "targeting key sectors of the U.S. economy." On Tuesday, another audio tape, purported to be the voice of bin Laden's senior deputy, Ayman al-Zawahri, repeated the threat.

The State Department alert issued late Thursday said, "We remind American citizens to remain vigilant with regard to their personal security and to exercise caution." It said that U.S. government facilities worldwide also remained at a heightened state of alert.

The alert said targets "may include facilities where Americans are generally known to congregate or visit," including clubs, restaurants, houses of worship and outdoor recreational events.

The alert was aimed at Americans worldwide and not limited to any specific country or region.