In pre-dawn raids, French police arrested seven people outside Paris in connection with the investigation into last week's attacks.
French authorities are probing a possible plot to attack the American embassy in Paris.
The seven individuals taken into custody are believed to have connections to an Algerian man arrested in Dubai, in the United Arab Emirates, in July, who has ties to Osama bin Laden, the Afghanistan-based terrorist whom President Bush has called a "prime suspect" in the Sept. 11 attacks.
The global dragnet also snared four men and one woman in London.
Scotland Yard announced that the suspects were arrested "in connection with the World Trade Center terrorist attack and are being questioned by Anti-Terrorist Branch officers."
The BBC's Caroline Thomsett reports that police raided a West London address at 3 a.m. this morning, arresting a 27-year-old man and a 25-year-old woman. At a separate address, around the same time, a 29-year-old was arrested. And then, at 7 p.m. this evening, a third man was arrested in Birmingham.
Back in the United States, the FBI today raided a home in Burlington, Ky., detaining about 20 people in connection with the deadly suicide hijacking raids.
Details are sketchy at this hour, but law enforcement sources said at least one of the hijackers lived in the Burlington area.
Warnings Issued to U.S. Industries
Authorities in the United States issued warnings to a number of American industries — including the petrochemical, nuclear and trucking industries, as well as Hollywood studios — about the possibility of future attacks.
Law enforcement officials tell ABCNEWS they believe there may have been as many as 30 attacks, both in the United States and overseas, planned by bin Laden's terrorist network, al Qaeda. More than two dozen terrorist suspects believed to still be in the country remain on the lam, sources said.
Attorney General John Ashcroft called acting Massachusetts Gov. Jane Swift and Boston Mayor Thomas Menino on Thursday to alert them to the threat of possible terrorist activity in Boston.
But Justice Department and local officials today downplayed the possibility of attacks on the city.
"We have … no new information that has caused us to be alarmed," Merino told reporters this afternoon. "There are no specific threats to the safety of the people of Boston."
Two of the flights hijacked on Sept. 11 originated in Boston.
"We do expect more attacks," a senior Bush administration official said Thursday. "We're at the point where anything is possible, but nothing can be predicted."
"We obviously have continuing concerns about the people responsible for Tuesday's attacks and information that does suggest they might have planned further attacks," added a senior intelligence official. "But we don't have any intelligence that gives us specific dates or methods for those attacks."
FBI Manhunt Continues
The FBI is continuing to pursue more than 200 people suspected of having ties to the hijackers, including as many as 30 who are believed to have had flight training.
ABCNEWS has learned that some of the individuals thought to have been trained as pilots had booked reservations on airline flights scheduled to take place in the days after last week's attacks — including flights out of Boston and San Antonio this coming weekend. They are from a variety of locations within the United States and all of them are believed to still be in the country.