Western intelligence officials have long feared such a scenario — a convert to Islam who is trained in terrorist methods and can blend in easily in Europe and the United States, traveling without visa restrictions.
Officials from three European security agencies confirmed Monday the man is "operational," meaning he has completed his training and is about to receive a target. All spoke on condition of anonymity because they were not authorized to discuss the case publicly. They declined to name the man, who has not been accused of a crime.
"We believe he is operational and he is probably about to get his target," one security official said. "And that target is probably in the West."
A security official in a second European country confirmed the information, adding: "From what I understand, a specific target has not been established."
CBS News correspondent Bob Orr notes that al Qaeda, for some time, has been trying to recruit and train western operatives who have the ability to travel freely and blend in with European and U.S. cultures.
Najibullah Zazi, a Denver airport shuttle driver, trained with al Qaeda terrorists in Pakistan and then returned to the U.S. with plans to bomb the New York City Subway. Faisal Shahzad, who lived in Connecticut, travelled to Pakistan to train with the Pakistani Taliban before returning with his failed plot to bomb Times Square.
In addition, Orr reports, several dozen U.S. citizens have travelled to Somalia to join the ranks of al Shabaab. U.S. officials continue to worry that some of them may some day attempt to return to the U.S.
Orr reports that U.S. officials have no specific information on the alleged Norwegian who is said to have trained in Yemen. But, one official said, "It's a plausible scenario."
European security services, including in Norway, have warned in recent years of homegrown radicalized Muslims traveling to terror training camps in conflict zones. Many of the known cases involve young men with family roots in Muslim countries.
But the latest case involves a man in his 30s with no immigrant background, the officials said. After converting to Islam in 2008, he quickly became radicalized and traveled to Yemen to receive terror training, one of the officials said. The man spent "some months" in Yemen and is still believed to be there, he said.
The official said the man has no criminal record, which would also make him an ideal recruit for al Qaeda.
"Not even a parking ticket," he said. "He's completely clean and he can travel anywhere."
The official would not specify what preventive measures were being taken but said "there is a well-established relationship between Western security services, and they share the information needed to prevent terrorism."
The officials declined to specify what makes them think the man is operational.
Signs that a would-be jihadist is ready for an attack could include the creation of so-called martyrdom videos for release online in conjunction with an attack, or an abrupt cutoff of communication and contacts with peers to avoid detection.
CIA and FBI officials in the U.S. declined to comment on the AP report.
Trond Hugubakken, a spokesman for Norway's PST security service, also declined to comment on the case. He referred to a PST security assessment in February, which highlighted that "several" Islamic extremists have traveled from Norway to conflict zones to attend training camps.
Hugubakken acknowledged that converts who turn to violent extremism pose a particular challenge.
"Converts will have a different level of cover, especially if they have no criminal record," he said, adding that most Muslim converts do not turn to extremism.
There are several examples in Europe and the U.S. of converts linked to terror plots, from failed shoe-bomber Richard Reid, a British convert, to a Pennsylvania woman dubbed "Jihad Jane," who pleaded guilty last year to charges that she plotted to kill a Swedish cartoonist who caricatured the Prophet Muhammad.
Norway saw the first convictions under its anti-terror laws this year when two men were given prison terms in January for plotting to attack a Danish newspaper that also had caricatured the Prophet Muhammad.
In March, Mullah Krekar, a radical Iraqi-born cleric who came to Norway as a refugee, was sentenced to five years in prison for making death threats against Norwegian officials and three Kurdish men he claimed had insulted Islam.
But Norway's most serious attacks happened last year at the hands of a right-wing extremist, Anders Behring Breivik, who admitted to killing 77 people in a bombing-and-shooting massacre on July 22. The self-styled anti-Muslim militant's trial ended last week with conflicting claims about whether he is criminally insane. A verdict has been set for Aug. 24.