Missiles, fighters ready to defend D.C.
Saudi foreign minister: 'This is our 9/11'
WASHINGTON (CNN) -- Another terror attack may be imminent, U.S. officials said Wednesday, with intelligence information pointing more toward an attack in the Persian Gulf region than the United States.
"I want to point out we had no specificity as to targets," said FBI Director Robert Mueller. "We had no specificity as to exact time."
Officials said intelligence gathered since last week's nearly simultaneous bombings at three residential compounds in Riyadh, Saudi Arabia suggests terrorists could strike in the "immediate future."
Meanwhile, the Pentagon has raised the "air defense posture" in the Washington D.C. area by deploying anti-aircraft missiles around the capital and stepping up air patrols over the city, defense officials told CNN Wednesday.
The steps have been taken in response to the overall increase in the national terror alert to orange or "high," officials said. (Flash gallery: Raising and lowering threat level)
A government official said one factor contributing to Tuesday's hike in the threat level was intelligence relating to the activities of al Qaeda members in Iran.
The government official, who asked not to be named, said the information about al Qaeda activities in Iran was "corroborated and credible," but did not relate to specific threats within the United States.
The official would not comment on the number of individuals involved, who they are or what their operational capability might be.
This information was one of many factors in the decision to raise the threat level and was part of a wide volume of information from a wide range of sources, the official said.
Iranian Foreign Ministry spokesman Hamid-Reza Asefi, on the Web site of the state-owned Islamic Republic News Agency, denied links to al Qaeda saying the country has no links to the "fundamentalist and violent" network.
In Washington, Army Avenger Systems are being placed at undisclosed locations, as they have been on at least two previous occasions since September 11, 2001.
The Avenger system consists of heat-seeking Stinger missiles mounted on HUMVEEs that are alerted by ground radar.
Pentagon officials say they have no specific threat against Washington, but the increased security measures are a prudent precaution, given the intelligence warning of an imminent terrorist attack somewhere in the world.
The air patrols are on an "irregulars" basis, officials said, and have been increased in conjunction with a previously scheduled training exercise announced by NORAD [North American Aerospace Defense Command] earlier this week.
The publicly announced exercise involves U.S. Air Force F-16s flying low over the Potomac River and parts of Maryland and Virginia between 10:30 p.m. and midnight on three days: May 21, May 29 and June 4.
Separately, the Defense Intelligence Agency increased its terrorism threat level from "significant" to "high," officials told CNN.
"High" is the top threat level, and means anti-U.S. terrorists -- who use large casualty producing attacks as their preferred method of operation -- are operationally active, and that the "operating environment favors the terrorist."
The threat assessment is issued to U.S. military commanders worldwide, who then are to review security procedures at their facilities and decide whether to increase the "force protection condition." (Full story)
September 11-style attack in Saudi Arabia planned
Saudi Foreign Minister Saud al-Faisal Wednesday said terrorists made "perhaps the biggest mistake" by targeting his country.
His comments came in the wake of last week's Riyadh bombings and the Wednesday arrests of three al Qaeda operatives suspected of planning a September 11-style attack in Saudi Arabia. However, Saudi television quoted Saudi Interior Minister Prince Nayef as denying there was a plot to hit a building with an airplane. (Full story)
"I've never seen this country united against something more than they are united against these terrorists," al-Faisal said. "They have seen the kind of purposeless hate and bloodshed that (terrorists) espouse, and everybody is against them."
He added, "This is our 9/11."
With the threat of more attacks in Saudi Arabia, he said authorities are taking "this news very seriously."
"We are preparing ourselves for the worst possible eventuality and hoping for the best," the foreign minister said.
Al-Jazeera: Top bin Laden deputy issues call to arms
On Wednesday, the Arabic-language television network Al-Jazeera broadcast an audiotape it said was from al Qaeda leader Osama bin Laden's top deputy, Ayman al-Zawahiri. On the tape, the speaker urged Muslims to target embassies of the United States and allies Great Britain, Australia and Norway.
"Learn from your brothers, the 19 that killed themselves in New York and Washington," the tape said in a reference to the September 11, 2001, attacks. "They achieved something that is unprecedented in history."
U.S. intelligence officials said they are analyzing the tape and do not know if it is authentic. (Full story)
Police chiefs across the country said they were increasing patrols and instituting other security measures. Commercial traffic from Canada into the United States was delayed two to three hours at key bridges near Buffalo, New York, and Port Huron, Michigan, amid more intense inspections.
• In Los Angeles, California, Police Chief Bill Bratton said patrols would increase around 605 "sensitive sites." However, he said the heightened security should not be obvious to most of the public. "Unless you were at the airport, you really wouldn't notice any change," he said.
• Seattle Police Chief Gil Kerlikowske said his officers were checking "some critical infrastructure and power grids" as well as keeping a watchful eye on the seaport in the heart of the Washington city.
• In New York, which has been on high alert since the system was established after September 11, the police commissioner said Tuesday he was stepping up uniformed police patrols, although the city has received no specific threats. (Full story) The heightened alert coincides with the start of the annual Fleet Week observances in New York, during which some 3,500 sailors and Marines are expected to be in the city for athletic competitions, receptions, concerts and free public tours of the ships. (Full story)
The Federal Aviation Administration announced that it would reimpose certain restrictions. These include bans on flying over stadiums or within 15 nautical miles of the Washington Monument, measures that have been put into place several times since the September 11 attacks. (Full story On the scene: CNN's Jeanne Meserve)
CNN Correspondents David Ensor, John King, Sheila MacVicar and Barbara Starr and Producer Terry Frieden contributed to this report.