U.S. counterterrorism officials say a key reason for raising the national terror alert on Tuesday had to do with the suspected activities of senior Al Qaeda (search) operatives thought to be in Iran (search) -- a country the Bush administration has long accused of harboring terrorists.
"There's no question but that there have been and are today senior Al Qaeda leaders in Iran, and they are busy," Defense Secretary Donald H. Rumsfeld told reporters Wednesday.
A surge in threatening communications, some given publicly, others intercepted covertly, was another critical factor, as were the recent attacks in Morocco (search) and Saudi Arabia (search), officials said.
Officials have identified five senior Al Qaeda operatives who they believe have been to Iran since the U.S.-led coalition ousted the Taliban from neighboring Afghanistan. Of those, officials believe some are still there, and the whereabouts of others is unclear. Those five comprise some of the most senior Al Qaeda operatives, below Usama bin Laden and his chief deputy, who remain at large.
The Homeland Security Department's orange alert suggests a high threat of terrorist attacks, and authorities extended security measures around the country.
The FBI warned anew Wednesday that the bombings in Saudi Arabia and Morocco could be a "possible prelude" to a terrorist attack in the United States and that attacks are "likely" against U.S. and Western interests abroad.
The warning was contained in an FBI bulletin sent weekly to more than 17,000 law enforcement agencies nationwide, marking the third time in six days the FBI has urged state and local police to increase their vigilance.
Using the same intelligence as the FBI, the Defense Intelligence Agency at the Pentagon informed regional commanders and commanders of military bases in the United States that the threat level was being raised from "significant" to "high," putting it at the highest of the DIA's separate, four-tier system, officials said.
Defense Department officials declined to say what other measures they were taking Wednesday, but during previous threats they've positioned anti-aircraft missile batteries near key sites in Washington and increased combat air patrols, flown by fighter jets over various American cities to intercept threats from the air.
FBI Director Robert Mueller and other officials acknowledged Wednesday the information was nonspecific, pointing to no particular time, target or method of attack.
American officials, generally describing intelligence information on the condition of anonymity, say they are suspected of connections to the bombings in Saudi Arabia and Morocco, which U.S. officials believe are part of a campaign to launch a wave of attacks to demonstrate Al Qaeda is still viable.
Officials cautioned their ties to those bombings are not certain, but said the information was still a major factor in the domestic alert. Another factor was information on terrorist plots gleaned from Al Qaeda prisoners abroad and corroborated by other intelligence.
Iranian officials deny harboring any Al Qaeda figures and say they captured scores fleeing Afghanistan and turned them over to Saudi Arabia.
Chief among those U.S. officials believe are in Iran is Saif al-Adil, an Egyptian described as bin Laden's security and intelligence chief. He may be the No. 3 Al Qaeda figure who remains at large.
Al-Adil orchestrated the training of Somali fighters who fought American troops in Mogadishu in 1993, was one of the key planners of the 1998 U.S. Embassy bombings in East Africa and is believed to have played a role in the planning of the bombing of the USS Cole, according to U.S. and British officials and documents.
Also believed to be in Iran is Abu Mohamed al-Masri, wanted for his alleged role in the Mogadishu and East Africa attacks, and Saad bin Laden, one of bin Laden's elder sons who officials have described as a rising star in Al Qaeda.
Two other top figures are believed to have been in Iran but their current whereabouts are uncertain. They are Abu Musab Zarqawi, the operational commander who the U.S. government tried to link to Saddam Hussein, and Abu Hafs the Mauritanian, a key ideological and religious counselor for bin Laden.
Why Iran would host some of the world's most wanted men is unclear. Some have suggested they want to trade them for members of the Mujahedeen Khalq, a resistance group opposed to Iran's religious government. Others say that hard-liners in the Iranian government may be sheltering them to drive a wedge between the United States and moderate elements in the Iranian government, who may not be aware the Al Qaeda figures are there.
Some threats in recent weeks from self-acclaimed Al Qaeda spokesmen are believed to be credible, U.S. officials said. In addition, private communications, intercepted by the United States, between suspected Al Qaeda operatives are another key factor.
Officials said they consider a new communication, purported from bin Laden's top deputy, Ayman al-Zawahri, as further evidence of possible terrorism. Previous messages from Al Qaeda leaders have sometimes heralded new attacks.
The speaker on the message singled out the United States, Britain, Australia and Norway. In response, the U.S. Embassy in Oslo, Norway, announced it would be closed to the public on Thursday.