LONDON, England (CNN) -- A deadly plan uncovered by Western intelligence services to attack targets across Europe could indicate a change in tactics by al Qaeda, security analysts say.
German intelligence officials say much of the information about the plot has come from a German citizen with suspected links to al Qaeda who was detained in Kabul in July and handed over to U.S. forces.
The officials say he has spoken of a plan similar to the 2008 assault on the Indian city of Mumbai and had told interrogators the plan had the blessing of Osama bin Laden.
In that attack, spread over three days, more than 160 people were killed as 10 men attacked and occupied a number of prominent buildings including the Taj Mahal Palace and Tower and Oberoi-Trident hotels, the city's Victoria Terminus train station, and the Jewish cultural center, Chabad House.
India blamed the attacks on the Lashkar-e-Tayyiba, a Pakistan-based terror group allied with al Qaeda.
With al Qaeda struggling to replicate attacks on the scale of the devastation witnessed on September 11, 2001 in New York and Washington, security experts believe the Mumbai attack, which gained worldwide publicity, may provide the template for its future operations.
"This new plot is perhaps an indication that al Qaeda is trying to change its strategy," said CNN's Senior International Correspondent Nic Robertson. "The high-profile attacks that it has always liked using explosives are clearly getting harder and harder to perpetrate.
"The cells are being spotted and it's harder to keep undercover when you're making bombs. Even buying the material to make bombs is getting harder, so many analysts believe al Qaeda would be unable to mount a 9/11-style attack in the current climate.
"Therefore Mumbai would have been viewed as successful by the al Qaeda leadership as it killed a large number of people. This type of attack is just as deadly but harder to stop."
In the last year, a number of plots targeting the West have been foiled, including the failed Christmas Day bombing of a U.S. airliner; the failed car bomb attempt in New York City's Times Square and an alleged plan to attack shopping malls in Manchester, England over one holiday weekend in 2009.
CNN Terrorism Consultant Paul Cruickshank says Western intelligence officials are extremely worried about a Mumbai-style attack if al Qaeda chooses "softer" economic targets.
"We're so vulnerable in Europe and the United States," he said. "Guns and ammunition can be concealed easily. They may be harder to access in Europe, but not impossible on the black market."
Last week, U.S. Homeland Security Secretary Janet Napolitano told the Senate Homeland Security Committee that the terrorism threat against the United States has evolved, with homegrown terrorists and a greater diversity in the scope and methods of attack -- making it more difficult to prevent them.
"It is diversifying in terms of sources; it is diversifying in terms of tactics," she said. "The results of these changing tactics are fewer opportunities to detect and disrupt plots."
Al Qaeda's hideouts in the tribal areas that straddle the Pakistan-Afghanistan border have come under greater pressure.
Operations by the Pakistani Army have forced the group into a diminishing area; and the much expanded U.S. drone campaign has disrupted its operations and killed senior figures. But enough of the leadership remains at large and it is a supremely adaptive organization.
"They're down but not out," warned Cruickshank. "Western counterterrorism officials believe Osama bin Laden signed off on this operation and this is a major fact to bear in mind.
"This is interesting because there has been little in recent times to pinpoint his role in various plots. So he's still in charge, he's still the strategic driving force but not the details guy.
"They may go to him for the big decisions but the detailed operations will be taken care of by people under him who have risen through the ranks in tribal areas of Pakistan, where it has its center, or have come recently from Europe or the U.S."
This diversification has also meant forging links with groups around the world that share al Qaeda's anti-western and jihadist ideology, such as al Shabaab in Somalia and Pakistan's Lashkar-e-Tayyiba.
"Al Shabaab is involved in a nationalist struggle in Somalia but has already shown it is willing to strike outside its borders with the recent attack in Uganda," said Robertson. "It has attracted people from the U.S. to go there and join the fight and al Qaeda would like to turn many of them around, creating a wider potential threat there."
Despite a number of failed plots, al Qaeda has retained a command structure -- and has a external operations chief planning operations around the world. U.S. officials say evidence of this emerged in the case of Najibullah Zazi, a U.S. resident, who this year confessed to a plot to carry out suicide bombings in the New York City subway.
U.S. officials allege that a senior al Qaeda handler, Adnan El Shukrijumah, recruited Zazi to conduct suicide bombings in the city with bombs made of hydrogen peroxide, acetone, and high explosive detonators.
An accomplice also confessed to being involved in the plot; a third man is due to go on trial in New York also accused of involvement. Prosecutors allege all three went to Pakistan and received training in making bombs at al Qaeda camps. Shukrijumah is a U.S. citizen who had lived in New York and Florida.
"Even though many al Qaeda plots failed, they have shown they can still send personnel to western countries, said Cruickshank. "The feeling is some attacks will eventually get through. Al Qaeda may be smaller now but they are still very capable of launching deadly attacks."