Updated

The government has failed to anticipate the danger from homegrown terrorists, some of whom immigrated to the United States, and now faces the most complex set of threats since the Sept. 11 attacks, analysts on an organization headed by the two 9/11 Commission co-chairmen warned Friday.

Unveiling a new report a day before the nation marks nine years since the 2001 attacks, members of the National Security Preparedness Group said Al Qaeda and other terror groups are increasingly turning to U.S. citizens to carry out attacks on the United States. They cited examples where recruiters went after Somali populations and other groups living in the United States, saying that while the U.S. at one time may have thought its cultural "melting pot" would provide a "firewall" against radicalization from within, that assumption turned out to be false.

"The United States has failed to fundamentally understand and prepare for these threats," group member Bruce Hoffman said. "Terrorists may have found our Achilles' heel. We have no strategy to deal with this growing problem and emerging threat."

The report said U.S. authorities failed to realize that Somali-American youths traveling from Minnesota to Somalia in 2008 to join extremist Muslim groups was not an isolated event. Instead, the movement was one among several instances of a broader, more diverse threat that has surfaced across the country.

As a result, there remains no federal agency specifically charged with identifying radicalization or working to prevent terrorist recruitment of U.S. citizens and residents, said the report.

The group, headed by former 9-11 commission leaders Tom Kean and Lee Hamilton, laid out a detailed description of domestic terror incidents such as the Fort Hood shooting spree last year in which 13 people died; the attempt to crash an airliner in December as it was landing at Detroit, Michigan; and last May's botched vehicle bombing in New York City's Times Square.

Kean told Fox News that Al Qaeda is serious about recruiting U.S. citizens and "non-traditional terrorists" to carry out its attacks.

"The threat is real, coordinated. It's something Al Qaeda wants to do now," he said. "They're moving to these smaller attacks. ... Everything becomes more possible if you have an American passport."

He said the United States needs to respond better to this evolving threat.

"We've got to attack it with the same energy and concerns and verve that we have ... in the past," Kean said.

During the past year, terrorism experts and government officials have warned of the threat posed by homegrown radicals, saying terror recruits who go abroad could return to the United States to carry out attacks.

But the United States, the report said, should have learned earlier from Britain's experience.

Before the 2005 suicide bombings in London's transit system, the British believed that Muslims there were better integrated, educated and wealthier than their counterparts elsewhere.

Similarly, U.S. authorities believed that its melting pot of nationalities and religions would protect it from internal radical strife, the report said.

The terrorists, it said, may have discovered America's "Achilles' heel in that we currently have no strategy to counter the type of threat posed by homegrown terrorists and other radicalized recruits."

U.S. officials have acknowledged the need to address the radicalization problem, and for the first time, the White House added combating homegrown terrorism this year to its national security strategy. The FBI, meanwhile, has worked to reach out to the Somali communities in an effort to counter the radicalization of the youth.

The report also points to an "Americanization" of the leadership of Al Qaeda and its allied groups, noting that radical cleric Anwar al-Awlaki, who encouraged the U.S. soldier accused in the Fort Hood shooting and others, grew up in the state of New Mexico. And Chicagoan David Headley played a role in scoping the targets for the Lashkar-e-Taiba attacks on Mumbai in late 2008 that killed more than 160 tourists and others.

Abroad, Al Qaeda, its affiliates and other extremist groups have splintered and spread, seeking havens in undergoverned areas of Pakistan, Yemen, Somalia and places in North and East Africa. That diversified threat has intensified as militants reached out to potential recruits through the Internet.

Assessing future threats, the report lists potential future domestic targets, including passenger jets, Western or American hotel chains, Jewish or Israeli sites and U.S. soldiers, even at their own bases in America.

It also warns that it is no longer wise to believe that American extremists will not resort to suicide bombings. They point to Maj. Nidal Hasan's alleged shooting spree at Fort Hood as an example, saying he had written about suicide operations in e-mails, and that his attack appeared to be one.

The Associated Press contributed to this report.