By Jane Standley BBC correspondent in New York

Civil rights groups in the United States have filed lawsuits against four American airlines, alleging that they "blatantly discriminated" against passengers because of their Middle Eastern or Asian origins.

United, Continental, Northwest and American Airlines are named in the proceedings, which are being brought by the American-Arab Anti-Discrimination Committee and the American Civil Liberties Union in the states of New Jersey, California and Maryland.

Since 11 September, airline security has increased

The lawsuits have been filed on behalf of four American citizens and a fifth man who is a legal permanent resident of the United States.

They say they were thrown off their flights simply because they looked to airline staff - or to passengers - to be from the Middle East, or to be Muslims.

There were no apparent security concerns, according to the civil liberties groups which are acting on their behalf.

Security risk

One man - who was born in Connecticut of Bangladeshi parents - claims he was not allowed to board a Northwest Airlines flight even after the Federal Bureau of Investigation (FBI) and other law enforcement agencies determined that he was not a security risk.

In another case, a man of Moroccan origin says he was removed from an American Airlines flight because a passenger felt uncomfortable with him on board - because he was an Arab with an Arab name.

The lawsuits ask the courts to stop airline staff from being able to overrule trained security personnel.

One airline is already being sued by a government secret service agent who was barred from flying because he is of Arab ancestry.