Updated 5:43 p.m. ET
European security officials said Wednesday a terror plot to wage Mumbai-style shooting sprees in Britain, France and Germany is still active and that sites in Pakistan - where the threat was intercepted two weeks ago - are being scoured for al Qaeda operatives.
CNN is reporting that al Qaeda leader Osama bin Laden himself "signed off" on the latest plan to target Europe. The CNN report cites and anonymous law enforcement source.
The plot was still in its early stages and not considered serious enough to raise the current terror threat level, officials said. Still, the Eiffel Tower in Paris was, the second time in the past week because of a bomb threat called in from a telephone booth.
CBS News has learned that the Dept. of Homeland Security's office of Infrastructure Protection sent out an e-mail Tuesday inviting private sector partners to a classified briefing "on recent overseas developments and Homeland threat reporting."
The threat is based mainly on European information and trends of reporting. There is nothing specific regarding times or locations of the attacks. The partner will be told that the concerns involve places of public gatherings such as hotels, parks, sports arenas and shopping mails. The information has the attacks carried out by small units or teams with weapons.
Meetings are scheduled over the next two weeks.
There is ample reason to be wary of the trumpeted terror warnings from European officials, reports CBS News correspondent Mark Phillips. Al Qaeda is not generally in the habit of giving warnings, via phone or any other means, in advance of their attacks, Phillips writes, and the current alarm seems to be aimed at drumming up support for unmanned drone attacks in tribal areas of Pakistan, where the alleged threat sprouted.
"This plot was in its embryonic stages," a British government official who spoke on condition of anonymity because of the sensitivity of his work told The Associated Press on Wednesday. "This one has preoccupied us more than others in the past few weeks - and it is still active - but it has not raised enough alarms to change our security threat level."
CBS News' Elaine Cobbe in Paris stresses that the new, alleged multi-country plot reported Wednesday has not led to any adjustments of the public terror threat level in France either. It has been at "red" for months, though the French Interior Ministry warned that increased vigilance was needed after the first alert at the Eiffel Tower, on Sept. 14 and other indications of a possible threat to the French transport network.
The terror threat level was raised earlier this month in France, where fears run high of a possible backlash from North African militants over attempts to ban the wearing of the veil by Muslim women in the country, Phillips reports.
According to reports attributed to security forces, al Qaeda affiliated groups were planning Mumbai-style commando attacks in western Europe - and onlyhave derailed those attacks by targeting the terror cells which have been planning them, Phillips reports.
Thein 2008 targets left 171 people dead, and was traced back to a terror group in Pakistan.
German television network RTL reported Wednesday that three suspects, all with dual German nationality, had been arrested in different countries and were providing the information leading to the warning.
The announcement of the plot came ahead of Thursday's anniversary of the Prophet Muhammad cartoons being published in a Danish newspaper.
It also came as Spanish authorities announced they had been.
Mohamed Omar Debhi, 43, was arrested Tuesday, although Spain's Interior Ministry said that was not connected to the terror threat. He is suspected of laundering money and sending some of it to an associate in Algeria, Toufik Mizi, to be passed on to cells of al Qaeda in the Islamic Maghreb.
Europe has been a target of numerous Islamic terror plots - the deadliest being the Madrid train bombings in 2004 when 10 shrapnel-filled bombs exploded during rush hour, killing 191 people and wounding about 1,800.
A year later, suicide bombers killed 52 rush-hour commuters in London aboard three subway cars and one bus.
In 2006, U.S. and British intelligence officials thwarted one of the largest plots yet and one that changed air travel forever - a plan to explode nearly a dozen trans-Atlantic airliners.
Officials gave no other details of the recent terror plot except to say that it originated in Pakistan with a group "threatening to wage a Mumbai-style attack" on cities in Britain, France and Germany. It was not clear how the attacks would be carried out or when.
In Washington, a Western counterterrorism official said some missile strikes in a recent surge of attacks by unmanned U.S. drones in Pakistan were aimed at disrupting suspected terrorist plots aimed at Europe.
Tim Marshall, of CBS News partner network Sky News, reported that some of the recent missile strikes had a direct link to the disrupted plot.
"The investigation in this plot has spread over the past two to three months, but the important leads came in the past few weeks," a European diplomat in Islamabad told CBS News' Farhan Bokhari.
The counterterrorism official said the targeted strikes were aimed at al Qaeda and other militant groups arrayed in Pakistan's tribal region near the Afghanistan border. The official spoke on condition of anonymity because the details of the terror plot remain sensitive.
The Obama administration has intensified the use of drone-fired missiles in Pakistan's border area, but this month there have been at least 21 attacks - more than double the highest number fired in any other single month.
A Pakistani government official, who also spoke on condition of anonymity Wednesday, said Pakistani officials had stepped up the search for suspected militants in the past two weeks.
"We are actively working with the Americans and British to stamp out these militants," he told the AP.
A suspected American missile strike killed four militants in northwest Pakistan on Tuesday, intelligence officials said. There was no word on the identities of those killed in the attack in the South Waziristan region, just across the border from Afghanistan. The Pakistani army last year launched a major anti-militant offensive in the region, though insurgents remain.
The counterterrorism official, who is familiar with the drone strikes and the details of the Europe terror plots, said Tuesday that the missile strikes in Pakistan are "a product of precise intelligence and precise weapons. We've been hitting targets that pose a threat to our troops in Afghanistan and terrorists plotting attacks in South Asia and beyond."
The official acknowledged that "our operational tempo has been up for a while now," and added that "given the stakes involved, we hope to keep the pressure on as long as we can."