WASHINGTON -- The FBI issued a worldwide alert Thursday for Adnan G. El Shukrijumah, a Saudi who government officials said may be plotting terrorist attacks against the United States as part of al-Qaida.

A senior law enforcement official, speaking on condition of anonymity, said the FBI believes the 27-year-old Saudi received flight training, possibly in Florida. A second senior source said El Shukrijumah possessed a Florida driver's license.

Officials said El Shukrijumah's organizing capabilities are comparable to those of Mohammed Atta, the suspected organizer of the Sept. 11 terror attacks. Fifteen of the 19 hijackers were Saudis and some, including Atta, received flight training in Florida.

The alert came as the FBI intensified its interviews with thousands of Iraqis in this country and, along with immigration agents, began arresting some on visa fraud violations. One official said the number of detainees was at least several dozen, but exact numbers weren't available.

The interviews were focused on about 11,000 Iraqi-born people in the United States who either have traveled to their homeland recently or had some contact with Iraq's military, law enforcement officials said.

The FBI is asking for help from law enforcement and the public in locating El Shukrijumah, who officials say may have been in the Miami area before he disappeared.

"El Shukrijumah is possibly involved with al-Qaida terrorist activities and, if true, poses a serious threat to U.S. citizens and interests worldwide," the FBI said in a statement.

In California, Highway Patrol Commissioner Dwight Helmick told reporters that police are double-checking tanker trucks that haul gasoline and other combustible substances because the suspect "has been known to utilize gasoline-type haulers" in the past. Helmick did not elaborate on that potential threat but said he had been briefed on the FBI alert.

El Shukrijumah is described as about 5-foot-4 and 132 pounds, though he may be heavier. He has black hair, black eyes and a Mediterranean complexion, and may be wearing a beard, the FBI said.

Although born in Saudi Arabia, the FBI said El Shukrijumah carries a passport from Guyana. He also could have passports from Saudi Arabia, Canada or Trinidad.

He has used many aliases, including Adnan G. El Shukri Jumah, Abu Arif, Ja'far Al-Tayer, Jaffar Al-Tayyar, Jafar Tayar and Jaafar Al-Tayyar.

The FBI alert did not specify the nature of the threats El Shukrijumah may pose. The senior law enforcement official said El Shukrijumah recently came to the FBI's attention based on information from one of the high-ranking al-Qaida leaders now in custody.

It was unclear if that information came from Khalid Shaikh Mohammed. Officials have described the March 1 capture of Mohammed, al-Qaida's chief operational planner, as a crucial breakthrough in the war on terrorism and have said he is providing useful information about al-Qaida operatives who may be in this country.

El Shukrijumah's brother Nabil told NBC that Adnan El Shukrijumah is neither a terrorist nor a pilot.

Meantime, the FBI has stepped up its interviewing of Iraqi-born individuals living in the United States to root out any potential terrorist attacks planned by Iraqi operatives or sympathizers. The FBI said the interviews also could help protect Iraqis from hate crimes.

Additionally, the FBI is actively investigating "others who have links to terrorism," including potential al-Qaida members or sympathizers in America.

Teams of FBI and immigration officials began arresting a number of Iraqis who are in the United States illegally, mainly for visa violations. A statement from the Bureau of Immigration and Customs Enforcement said the operation was aimed at "taking individuals off the street who might pose a threat to the safety and security of the American people" and said they were targeted based on intelligence information.

Several thousand FBI agents are being diverted from regular duties to do the interviews and to man command posts at each of the bureau's 56 field offices. They are to gather intelligence and respond quickly to any terrorist threats. A national command center was set up at FBI headquarters in Washington.

"We are bringing to bear the full weight of our resources, expertise, and partnerships," FBI Director Robert Mueller said. "We are running down every lead, responding to every threat, coordinating with every partner, and doing our utmost to keep terrorists from striking back."

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