Updated

Various terrorist cells are plotting to strike again in the U.S. and abroad, government officials say.

The officials, speaking only on condition of anonymity, said intelligence reports on potential new threats to U.S. interests have grown in quality and quantity over the last week.

The evidence doesn't point to specific targets, but indicates that several cells are waiting to attack.

Over the last month, 225 people overseas have been rounded up in about a dozen countries based on U.S. and foreign intelligence indicating they were involved in plotting or assisting terrorism, the officials said.

The FBI believes several people involved in plotting remain at large in the United States and across Europe and the Middle East, the officials said.

Overseas, U.S. officials working with foreign governments have identified and disrupted plans to bomb four U.S. diplomatic and military sites, the sources said.

The officials said the plots involved attacks on the U.S. Embassy in Paris, an American building in Turkey, embassy structures in Yemen and a NATO building in Brussels, Belgium.

Yemeni authorities have been searching for a dozen Arabs, several connected to Usama bin Laden's Al Qaeda network, who entered the country from Afghanistan after the Sept. 11 terrorist attacks, officials said.

Attorney General John Ashcroft said Sunday the FBI still is searching for about 190 people it believes may have involvement or information.

"We have a watch list of individuals that we want to apprehend and question and to ascertain with more specificity the extent to which they have knowledge of, or might be in some way related to, either the groups or the actual incidents," Ashcroft said.

Asked about the scope of the threat now, one U.S. official compared it to the millennium celebrations in December 1999 when the CIA and other intelligence agencies identified and disrupted between five and 15 potential attacks. Those plots included a hotel in Jordan and the Los Angeles airport, and several bin Laden supporters were rounded up in different countries to thwart the activities, officials said.

Officials said much of the evidence suggests various loosely knit terrorist cells — from Algerians to Afghans — are agitating to attack again. They're united in their admiration for bin Laden and his calls to attack Americans, but there is no evidence they are being coordinated in a single master plan, the officials said.

Some have trained or received assistance from Al Qaeda, the officials said. Others have been linked to bin Laden supporters through financial transactions and communication intercepts, officials said.

Law enforcement officials said they have evidence — some vague, some more specific — that Middle Eastern men have been scouting targets from nuclear power plants and airports to embassies overseas and tourist locations.

The officials cautioned they haven't identified a specific threat or plan against a U.S. interest out of the 573 threats that have been processed by the FBI, but if they do, a public warning will be issued.

"We will share with the appropriate parties and the American people credible threats," Ashcroft said.

The recent foiled plans overseas highlight one assessment of U.S. intelligence about the methods of bin Laden and Al Qaeda: they persist in striking targets missed in earlier attempts. The World Trade Center in New York was bombed in 1993, but without mass casualties; it was leveled in the Sept. 11 attacks.

Between May and July, American intelligence braced for a wave of attacks by bin Laden supporters overseas and helped disrupt terrorist plans for attacks on U.S. embassies in Yemen and France and a site in Turkey, a U.S. official said.

Still concerned about the possibility trucks could be used for bombings, the FBI also has checked student records at a Colorado truck-driving school, classroom instructor Jack Atencio said. Agents visited the school in Henderson, just northeast of Denver, for a few hours last week, checking specific names, Atencio said.

The FBI is searching anew for Khaled Alzeedi, a Saudi pilot who purchased two small aircraft in August from an airplane broker in Clarksville, Tenn., and left the state shortly before the suicide hijackings, according to records and interviews. Clarksville is near Fort Campbell, Ky., where some of the U.S. elite special forces are stationed.

Alzeedi's name appears on a list of people wanted for questioning in the investigation, but Assistant FBI Director John Collingwood said Sunday that the interest in him has to do with something "totally unrelated to the hijackings."

The Associated Press contributed to this report.