The man accused of trying to blow up a U.S.-bound airliner was not flagged in Britain as a potential terror suspect — he was merely put on a standard watch list of people whose visa applications were rejected, British officials said Monday.

Umar Farouk Abdulmutallab, a Nigerian who had graduated from a London university last year, had his subsequent visa application denied in May 2009. Government officials said the school on his application form was not a government-approved institution.

People who have visa applications refused in the U.K. are placed on a watchlist, which is then divided into different categories depending on the risk they pose to Britain. Abdulmutallab's name was placed on the list as a matter of routine, not because he was thought to pose a threat, according to a spokeswoman for the Home Office who spoke on condition of anonymity in line with government policy.

She added that there are some 2,000 schools in Britain accredited to receive international students, and that the school Abdulmutallab had claimed to enroll in was not one of them. Citing security reasons, the spokeswoman refused to reveal the institution's name or location of the college but said the institution is being investigated by authorities.

Home Secretary Alan Johnson said U.S. authorities should have been informed that Abdulmutallab had been placed on the U.K.list and believed all procedures had been followed correctly.

Abdulmutallab received a degree in engineering and business finance from University College London last summer and later applied to re-enter Britain to study at another institution. The Home Office spokeswoman declined to reveal the dates in which Abdulmutallab entered and left the U.K. but said he held a valid visa between 2005 and 2008 — the period of time when he was studying at University College London.

In a statement, the university said it was "deeply shocked" by the news about Abdulmutallab. Its engineering department described him as a "well mannered, quietly spoken, polite and able young man" who never gave his tutors any cause for concern.

The use of non-accredited schools to secure student visas has been identified as a weakness in Britain's immigration system.

In April, one of several suspected terrorists arrested in raids in northern England was found to have a visa issued with the help of a non-accredited college, prompting opposition lawmakers to call for a crackdown. Last week Britain's immigration minister Phil Woolas boasted that the government had closed some 2,000 fraudulent schools.

British police and security services, meanwhile, were looking at whether Abdulmutallab was radicalized in Britain.

"We don't know yet whether it was a single-handed plot or (there were) other people behind it —I suspect it's the latter rather than the former," Johnson told the British Broadcasting Corp.

The East London Mosque — one of Britain's largest mosques — dismissed reports that it was connected to Abdulmutallab and his attempt to blow up an airliner.

Ayub Khan, a member of the mosque's board of directors, said he was "appalled by the alleged actions of this individual." He added that 20,000 people attend the mosque each week and that he did not know whether Abdulmutallab had attended any of the prayers.

British authorities have closely monitored many of the country's nearly 2 million Muslims after the July 7, 2005 suicide bombings that killed 52 people on London's transit system.

Abu Hamza al-Masri, a former imam at London's Finsbury Park Mosque, was jailed for seven years for inciting racial hatred and encouraging followers to kill non-Muslims. Finsbury Park Mosque also said it is not aware of any connections with Abdulmutallab.

The Muslim Council of Britain condemned the attempted bombing.

"The connections to the U.K. are equally disturbing and today the MCB urged calm on all sides," said the Council's Secretary General Muhammad Abdul Bari. "There are approximately 100,000 Muslim students at universities across the U.K. — the vast majority of whom are law-abiding and play a full and active role in student life. Muslim students, who come to study in the UK from across the world have contributed immensely to the culture, society and economy of the U.K."