The US was slow to take seriously the threat posed by homegrown radicals and the government has failed to put systems in place to deal with the growing phenomenon, according to a new report.
The report says US authorities failed to realise that Somali-American youths travelling from Minnesota to Mogadishu in 2008 to join extremists was not an isolated issue.
It was one among several instances of a broader, more diverse threat that has surfaced across the country, says the report by the former heads of the September 11 Commission.
"Our long-held belief that homegrown terrorism couldn't happen here has thus created a situation where we are today stumbling blindly through the legal, operational and organisational minefield of countering terrorist radicalisation and recruitment occurring in the United States," said the report.
As a result, there is still no federal agency specifically charged with identifying radicalisation or working to prevent terrorist recruitment of US citizens and residents, said the report, to be released by the Washington-based Bipartisan Policy Centre's National Security Preparedness Group.
The group laid out a detailed description of domestic terror incidents ranging from the Fort Hood, Texas, shooting spree and the attempted Christmas Day airliner attack in late 2009 to last May's botched truck bombing in New York's Times Square.
Over 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 US to carry out attacks.
But the US, the group said, should have learned earlier from Britain's experience. Before the 2005 London suicide bombings, the British believed that Muslims there were better integrated, educated and wealthier than their counterparts elsewhere.
Similarly, the US believed that its melting pot of nationalities and religions would protect it from internal radical strife, the report said. It added: "The terrorists, said the report, 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 radicalised recruits."
US officials have acknowledged the need to address the radicalisation problem, and for the first time, the White House this year added combating home-grown terrorism to its national security strategy.