Washington ? The FBI issued a worldwide alert Friday for four men linked to al-Qaida, including a suspected terror cell leader and an avowed suicide attacker, after new intelligence indicated they might be plotting attacks against the United States.

The bulletin came amid an increase in intelligence chatter that suggested heightened 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.

Intelligence corroborated by multiple sources, including foreign governments and law enforcement officials, led the FBI to post on its Web site the names and photographs of two Saudis, a Moroccan and a Tunisian sought for questioning.

Federal law enforcement officials said the FBI was hoping someone in the United States or abroad would recognize one or all of 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:

l 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 says 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.

l 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.

l 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.

l 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.