U.S. counterterrorism officials say they believe that senior al Qaeda leaders, including Osama bin Laden, are involved in the latest against European cities.
The multipronged scope of the emerging plan - which aimed to launch coordinated shooting sprees or attacks in Britain, France and Germany - is an al Qaeda hallmark. One U.S. intelligence official added, however, that the details of how the plan was directed or coordinated by the group's core leaders is not yet clear.
The involvement of bin Laden and his core leaders, believed to be in hiding in Pakistan, underscores concerns about that country's role as a haven for al Qaeda and other Islamic extremists. U.S. officials have pressed Pakistan to increase its efforts to root out the militants hiding in the mountainous border region.
Several officials spoke on condition of anonymity to discuss intelligence information.
Bin Laden's role in the European plot was first reported by NPR.
Counterterrorism officials said that they are now working under the assumption that bin Laden played a role in the plotting, but they would not detail what indications they've seen that lead them in that direction.
One senior U.S. official, meanwhile, discounted any involvement in the Europe terror plot by al Qaeda's North African affiliate. While al Qaeda in the Islamic Maghreb is very dangerous in its region and may want to export its terror operations to Europe, there are no indications that it is able to do that at this time, said the official.
A Pakistani intelligence official said Thursday that , which is still in its early stages. One of the Britons was killed in a recent CIA missile strike, he said.
Pakistan, Britain and Germany are tracking the suspects and intercepting their phone calls, the official told The Associated Press on condition of anonymity because he was not authorized to release the information to the media.
Western security officials said earlier this week that a terror plot to wage Mumbai-style shooting sprees or other attacks in Britain, France and Germany was still active. Both European and U.S. officials said the plot was still in its early stages and not considered serious enough to raise the terror threat level.
Still, the Eiffel Tower in Paris was briefly evacuated Tuesday - the second time in two weeks because of an unspecified threat - and there was a heavy police presence around Buckingham Palace, Trafalgar Square and Big Ben. Police on Thursday evacuated a street near Britain's Parliament in London after reports of a suspicious vehicle but said they did not regard the incident as serious.
Nevertheless, the dramatically trumpeted foiled plot in Europe may be in part a political ploy to raise support for more unmanned drone strikes in Pakistan.
The U.S. has dramatically stepped up its missile attacks in North Waziristan, and is believed to have launched at least 21 this month. The covert campaign is largely carried out by CIA drones, and has led to the deaths of a number of top militant leaders.
Pakistan has complained vocally about the program but is believed to provide intelligence assistance for at least some of the strikes.
French authorities, meanwhile, have received indications from allied intelligence services about the possibility of attacks, but no plot outright, a high-ranking French security official said on condition of anonymity because of the sensitivity of the issue.
A recent spate of anonymous, phoned-in bomb threats in Paris - including on the Eiffel Tower - didn't appear to have the "signature" of al Qaeda, the official said, noting the terror network hasn't typically tipped off authorities to attacks in advance.
In related news, Sweden has from low to elevated because of "a shift in activities" among Swedish-based groups that could be plotting attacks against the Scandinavian country, security officials said Friday.
The Swedish Security Service, SAPO, declined to say whether the threat involved Islamic terrorists or if it was linked to the broader European terror threat.
SAPO said the terrorism threat remained low in Sweden compared with other European countries, and that no attack was imminent.
Earlier Friday, bin Laden to help Muslims in an audiotape released Friday, seeking to exploit discontent following this summer's devastating floods in Pakistan by depicting the region's governments as uncaring.