(CNN) -- The men allegedly behind last week's failed terror plots in England and Scotland have connections to al Qaeda in Iraq, U.S. officials said Tuesday.
At least some of the suspects were recruited by al Qaeda while they were living in the Middle East, the sources said.
Al Qaeda has been trying to recruit people who can travel easily to the United States and Europe and assimilate into society without causing suspicion, according to law enforcement officials.
Counterterrorism officials told CNN they believe the plots in Britain may be a blueprint for attacks on the United States. But, the officials say, the degree of what might be in the works and timing of any potential attack remain unknown.
"Some wonder why they just don't do vehicle bombs here. It would certainly cause panic and terror, and soft targets do exist here in abundance. But I continue to think they don't want to waste their shot here on something that isn't fairly spectacular," one counterterrorism official said.
"There's a strong conviction we are vulnerable here," another official said. "They are planning and trying to put something together, and given that these are people who play by no rules, are willing to die -- it doesn't matter how much we harden targets, they will still find some way to get through."
"The next attack here is likely to focus on some sort of infrastructure," a third counterterrorism official said.
The counterterrorism officials spoke to CNN on condition of anonymity because of the sensitivity of the story.
Seven of the eight people arrested are doctors or medical students and the other is a laboratory technician. Two other doctors are being questioned about the case but are not in custody
British police identified Iraqi physician Bilal Abdulla, 27, as one of the two men suspected of leaving two car bombs in central London on Friday and ramming an explosives-laden sport utility vehicle into a terminal at Glasgow Airport on Saturday.
British media were reporting Tuesday that the other person in the SUV was Dr. Khalid Ahmed. His country of origin or nationality is not known. This second man was severely burned in the Glasgow attack and is in critical condition at the city's Royal Alexandra Hospital.
Media are also reporting that a man taken into custody Sunday in Liverpool is Sabeel Ahmed, 26, who trained as a doctor in India.
Seven people are in custody in Britain and at least one has been detained in Australia.
Australian Foreign Minister Alexander Downer said a 27-year-old Indian national, identified in British media reports as Dr. Mohammed Haneef, had been detained at an airport in Brisbane, Queensland, "in the context" of the British investigation. He reportedly was holding a one-way ticket to India.
Australian Prime Minister John Howard said Haneef was working in the country on a temporary visa.
"He was sponsored by the Queensland Health Department," Howard told a news conference. "He was working as a registrar at the Gold Coast Hospital."
Haneef previously had worked at Halton General Hospital, near Liverpool in northwestern England, where the man taken into custody Sunday was employed, according to hospital and police officials.
A second doctor in Australia was being questioned but had not been detained in police custody, according to Queensland Premier Peter Beattie. Watch how the probe has led to Australia »
Beattie said both doctors were recruited from Liverpool last year, through an advertisement in the British Medical Journal, to work in Australia.
The doctor who was in custody was considered a good employee in the emergency department and was "regarded as a model citizen, excellent references," Beattie said.
Sources said one of the two suspects behind the Glasgow attack worked as a doctor at the Royal Alexandra Hospital, although it is not clear which one.
Police also arrested Dr. Mohammed Asha, a Jordanian-educated physician who moved to England two years ago, according to a source with knowledge of the investigation.
Asha, 26, was picked up late Saturday on a motorway in the Cheshire area of northern England, a source said. Police said he was arrested with a 27-year-old woman, identified by Asha's family as his wife.
Asha's house in Newcastle-under-Lyme, Staffordshire, has been searched since his arrest Saturday night. Neighbors there said another doctor was also part of the investigation.
Police had sealed the home of the unnamed doctor and his wife, which is about two miles from Asha's home. Forensic teams were searching the house, where the unnamed physician and his wife had lived for about a year, neighbors said. Police search for evidence in the terror scares »
It was unclear if those two were in police custody.
Counterterrorism officials note doctors' expertise in biology and chemistry and have access to radiological material such as medical isotopes, could be used in terrorist acts.
According to officials, there has been long-standing concern that Iraq is a breeding ground for a new generation of terrorists who have been testing tactics of urban warfare, which can then be used in Western nations.
Terrorism analyst Marco Vicenzino, the director of the Global Strategy Project, says the world could be seeing a shift in jihadist tactics.
Confident after wounding the United States and its allies in Iraq, jihadists "are determined to take their combat experience directly to the superpower and its allies at home and around the world," Vicenzino said. E-mail to a friend
CNN's Kelli Arena, Andrew Carey, Matthew Chance, Paula Newton, Cal Perry, Nic Robertson and Alphonso Van Marsh contributed to this report.