KEF: KEFLAVIK, ICELAND LONDON (Jan. 19) - A passenger jet flying from Britain to Florida with 340 people on board was diverted to Iceland on Saturday after the crew found a bomb threat and anti-American messages scrawled on a bathroom mirror in soap. A spokesman for Virgin Atlantic Airways indicated the incident was a hoax. ''It is a shame that people are being disrupted by someone being a bit silly,'' spokesman Ben Hall said. The Boeing 747 landed safely at Keflavik airport, 30 miles southwest of the capital Reykjavik, about six hours after it took off from London's Gatwick airport bound for Orlando, Fla, officials said. It had 322 passengers and 18 crew on board. Keflavik Police Commissioner Johann Benediktsson said the threat was written in soap on a mirror in a plane toilet. ''It contained the phrase 'all Americans must die' and other anti- American sentiment,'' he said. It was not immediately known who wrote the threat. Airline spokesman Ben Hall said none of the passengers would be allowed to leave the airport until they had been questioned by police. Dozens of fire engines and support vehicles from the nearby U.S. naval base at Keflavik were sent to the airport and ambulances in Reykjavik were placed on standby, said Fridthor Eydal, spokesman for the base. The passengers were led into an auxiliary fire station near the terminal building, Eydal said. ''The hand luggage is going to be searched and all passengers will be searched,'' he said. Virgin spokesman Hall said the pilot regarded the situation as a low-level security threat, but decided to divert the plane as a precaution. He said the passengers would be put up overnight in a hotel and would be on their way in the morning. Leo/ORD