U.S. troops on alert for possible strike by bin Laden followers

Osama bin Laden is thought to be living in Afghanistan

WASHINGTON (CNN) -- U.S. troops in the Mideast spent a second day on high alert on Saturday for a possible attack by followers of alleged terrorist Osama bin Laden, sources tell CNN.

In addition, the U.S. State Department said it was cautioning U.S. citizens abroad of an "increased risk."

The alert is in response to a "nonspecific but credible threat" from bin Laden's group, sources told CNN.

The threat is believed to be against U.S. citizens and interests around the world, rather than specifically against the U.S. military or potential targets in the Persian Gulf region, according to CNN sources.

VIDEO CNN's David Ensor reports on what the U.S. is doing to protect itself from an increased terrorism threat (June 22) Play video (QuickTime, Real or Windows Media)   INFORMATION Naval forces in the Persian Gulf     MESSAGE BOARD Security threats     ALSO U.S. to caution against 'increased' travel risk  Bin Laden associate arrested in Spain  Iran rejects U.S. Khobar allegations  Khobar Towers indictments returned

Bin Laden has been indicted by the United States for allegedly masterminding the 1998 bombings of U.S. embassies in Nairobi and Dar es Salaam that together killed 224 people. U.S. authorities also suspect bin Ladan was behind a suicide bombing of the Navy destroyer USS Cole that killed 17 U.S. servicemen and women and injured 39 in the attack on October 12, 2000.

The exiled Saudi millionaire is believed to be taking refuge in Afghanistan, where the ruling Taliban movement has refused to turn him over to Western powers.

A videotape that surfaced on Thursday showed bin Laden delivering a message to his supporters. "To all the Mujahedeen, your brothers in Palestine are waiting for you, it's time to penetrate America and Israel and hit them where it hurts most."

Officials said U.S. intelligence had indications from two separate sources that an attack was planned, and had monitored the movement of known bin Laden operatives.

The threat "does not point to a specific region," according to an informed U.S. official who spoke on the condition of anonymity. The official said the threats are concentrated in the Middle East and Persian Gulf, but that the increased risk is worldwide.

The officials said there was a time frame for the attack, but they would not disclose it.

But one official said the attack appeared to have been planned before Thursday's announcement of U.S. indictments against 14 suspects in the June 25, 1996, bombing of the Khobar Towers housing complex in Saudi Arabia that killed 19 U.S. airmen and injured hundreds of others.

Thirteen Saudis and one Lebanese citizen are accused of bombing the military housing complex. The fifth anniversary of the bombing is Monday.

Monday is the fifth anniversary of the Khobar Towers bombing

Ships of the U.S. 5th Fleet, including the USS Constellation aircraft carrier group, put out to sea on Friday as a precaution under the requirements of the heightened alert.

Most of the fleet was already at sea, but some minesweepers left port from Bahrain, headquarters of the U.S. 5th Fleet.

State Department officials said the U.S. Embassy in Bahrain will not reopen Saturday (which is the first day of the working week in the region) and the U.S. Embassy in Dakar, Senegal, closed early Friday because of security concerns.