He is expected to have an acute understanding of terrorist groups and their threats to American interests. But the incoming chairman of a congressional intelligence committee was yesterday struggling to explain his ignorance of Al Qaeda and Hezbollah.

Silvestre Reyes, the Democrat chosen to head the House of Representatives committee, was asked whether members of Al Qaeda came from the Sunni or the Shia branch of Islam.

"Al Qaeda, they have both,” he answered, adding: “Predominantly probably Shi’ite.”

In fact, Al Qaeda was founded by Usama bin Laden as a Sunni organisation and views Shia Muslims as heretics. The centuries-old now fuels the militias and death squads in Iraq.

Jeff Stein, a reporter for Congressional Quarterly, then put a similar question about Hezbollah, the Lebanese Shia group. “Hezbollah. Uh, Hezbollah . . .” replied Mr Reyes. “Why do you ask me these questions at five o’clock? Can I answer in Spanish? Do you speak Spanish?” Go ahead, said Stein. “Well, I, uh . . .” said the congressman.

His apparent ignorance of basic facts have raised fresh questions over his suitability for the key intelligence post — as well as the judgment of Nancy Pelosi, the new Speaker of the House, who picked him for the job. She has already been criticised for trying to oust her deputy Steny Hoyer, in a poll among Democrat congressmen after the mid-term elections.

There was further controversy over her choice of Mr Reyes over the head of Jane Harman, who had been the committee’s most senior Democrat but was said to have upset Ms Pelosi. At the time Mr Reyes said he had “very strong credentials” for the job — “credentials which could stand up to anybody”.

Yesterday he said in a statement: “The CQ interview covered a wide range of topics other than the selected points published in the story. As a member of the intelligence committee since before 9/11, I’m acutely aware of Al Qaeda’s desire to harm Americans. The committee will keep its eye on the ball, and focus on the pressing security and intelligence issues.”

Earlier this year Stein flummoxed two Republicans on the committee, Jo Ann Davis and Terry Everett, with similar questions about the differences between Sunni and Shia. “One’s in one location, another’s in another location. No, to be honest with you, I don’t know,” replied Mr Everett.

Stein has also caught out Willie Hulon, chief of the FBI’s new national security branch when he was asked to which branch of Islam were Iran and Hezbollah belonged. “Sunni” he replied. “Wrong,” said Stein.

Stein has defended his use of such questions: “To me, its like asking about Catholics and Protestants in Northern Ireland — who’s on what side? Its been five years since these Muslim extremists flew hijacked airliners into the World Trade Centre. Is it too much to ask that our intelligence overseers know who they are?” Indeed, Trent Lott, No 2 in the Republican Senate leadership, said recently: “It’s hard for Americans, all of us, to understand what’s wrong with these people . . . They all look the same to me.”

The report from the Iraq Study Group expressed amazement that more was not being done to “understand the people who explode roadside bombs”. Only six people in the US Embassy in Baghdad are fluent in Arabic, about two dozen of its 1,000 employees having some familiarity with the language.