WASHINGTON -- The FBI is enlisting the world's help to find four men suspected of ties to al-Qaida, including a possible terror cell leader and an avowed suicide attacker.

The FBI posted a "seeking information" alert for the four on its Web site Friday after intelligence corroborated by multiple sources, including foreign governments and law enforcement officials, indicated they might be plotting new attacks against the United States.

The bulletin came amid an increase in intelligence chatter suggesting increased terrorist activity as the second anniversary of the Sept. 11 attacks nears. Still, the government has not uncovered a specific threat or plot that would warrant raising the national terror threat level from its current elevated status.

Federal law enforcement officials said the FBI is hoping someone in the United States or abroad will recognize one or all the men. Officials have no evidence any are in the United States, but because they all have used false names and travel documents in the past, the possibility cannot be ruled out.

The officials, speaking on condition of anonymity, cautioned that it was unclear if the four men were working together. There was no information they were involved in a specific terrorist operation.

The four being sought are:

--Adnan G. El Shukrijumah, 28, a Saudi native who lived for a number of years in South Florida. The FBI has been searching for him for months, and officials say he could be a terror cell leader or organizer similar to Mohamed Atta, a top planner of the Sept. 11, 2001, attacks and pilot of one of the hijacked planes.

The FBI bulletin said federal prosecutors in northern Virginia have obtained a warrant to detain El Shukrijumah as a material witness, which normally is kept secret. The FBI says he is of particular interest because of his familiarity with the United States, ability to use fake documents and fluency in English.

--Abderraouf Jdey, 38, born in Tunisia, was naturalized a Canadian citizen in 1995 and might have a Canadian passport. Jdey was among five men who left suicide messages on videotapes recovered at the Afghanistan residence of Mohammed Atef, Osama bin Laden's military chief who was killed in a U.S. air strike. Also recovered was a suicide letter in which Jdey promised to die fighting non-Muslim infidels.

--Karim El Mejjati, 35, a Moroccan who holds a French passport. His last recorded entry into the United States was between 1997 and 1999. Officials say El Mejjati may have been involved in the May 16 suicide bombings in Casablanca, Morocco, that killed 45 people.

--Zubayr Al-Rimi, 29, a Saudi native. The only clue given publicly by the FBI is the identity of his wife, a Moroccan named Hanan Raqib.

Posting the names and photos of all four on the Internet also allows the FBI to spread the word globally, including into lawless areas of Pakistan and Afghanistan where many al-Qaida operatives are believed to be regrouping, officials said.

The alert follows a bulletin from the Homeland Security Department that stressed al-Qaida "continues to develop plans for multiple attacks" against U.S. interests using commercial aircraft. More than 3,000 people died on Sept. 11, 2001, when four hijacked jets were crashed into the World Trade Center towers, the Pentagon and a Pennsylvania field by 19 al-Qaida operatives.

Intelligence has revealed that al-Qaida has been studying ways to hijack airliners as they flew over or near the United States and has been examining international airports to identify those with the least stringent security and visa requirements.

Al-Qaida also may try simpler methods it has used overseas, such as a suicide truck bomb, and it may try to target infrastructure such as nuclear plants, transportation systems, water reservoirs or dams, food supplies or the nation's electric grid, the bulletin said.

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On the Net:

FBI: http://www.fbi.gov

Homeland Security Department: http://www.dhs.gov