Officials of an American airline have been forced to admit their embarrassment after allowing a pig to travel first class on a flight from Philadelphia to Seattle.

The animal -- said to weigh about a hundred and fifty kilos -- was taken onto the flight by two women.

They had told staff of US Airways that they had a doctor's note describing the pig as a service animal -- roughly similar in function to a guide dog.

But passengers complained when the animal started squealing and became unruly during the flight.

An airline spokesman pledged that such an incident would never happen again.

From the newsroom of the BBC World Service