British intelligence officials knew that the Nigerian man suspected of trying to bomb a Detroit-bound airliner had ties to U.K. extremists but did not consider him enough of a high risk to alert American authorities, a senior British official said Sunday.

Officials realized about a year after Umar Farouk Abdulmutallab came to London to study in 2005 that he was in contact with Islamic extremists whose communications were being monitored, a senior government official told The Associated Press on Sunday.

But there were no signs that Abdulmutallab wanted to target the United States or was considering turning toward violence, the official said, speaking on condition of anonymity because of the sensitivity of his work.

"It was clear he was reaching out to radical extremists in the U.K. but there was nothing to indicate he was violent," the official said. "There is a very large number of people in the U.K. who express interest in radical extremism but never turn to violence. He only pinged up on our radar because of other people we were interested in."

Officials say Abdulmutallab, a 23-year-old Nigerian who spent time in Yemen, sneaked an explosive device aboard his Northwest Airlines flight from Amsterdam to Detroit on Christmas Day but was not able to ignite it as planned.

President Barack Obama has said there was a systemic failure to prevent the attack and ordered a thorough review of security shortcomings. The president has summoned Homeland Security officials to meet with him in the White House on Tuesday.

The British official said even though there are no set profile characteristics to indicate whether a suspect is likely to turn violent, the overall risk a person poses can be assessed by looking their associates, travel patterns, threats and activities.

He declined to name the extremists that Abdulmutallab had contacted.

"Obviously if there was any indication that he was likely to target the U.S., we would have immediately alerted our U.S. counterparts," the officials told The Associated Press in an interview. "But the fact is that many start on this journey of extremism and few complete it."

He said it wouldn't make sense to alert US authorities to every person who showed up on the "fringes of extremism" and said Abdulmutallab's actual radicalization appeared to have come in the time he spent in Yemen.

It is believed Abdulmutallab received training in Yemen five months before the failed attack.

A U.S. intelligence official said American counterterrorism officials are looking into what knowledge allies may have had about Abdulmutallab. He spoke on condition of anonymity because he was not authorized to publicly discuss foreign intelligence.