SYDNEY, Australia —  A written bomb threat forced a United Airlines (search) jet to return to Sydney International Airport (search) on Tuesday after it took off for Los Angeles, but police declared the threat a hoax after interviewing all 246 passengers.

The hoax occurred days after a purported Al Qaeda affiliate in Europe, the Tawhid Islamic Group (search), warned it would turn Australia into "pools of blood" if the government did not withdraw its troops from Iraq. Australia has nearly 900 military personnel in the region.

Transport Minister John Anderson told Australian Broadcasting Corp. radio the "object" discovered was a note carrying a bomb threat. He said the threat was being investigated.

Australian media reported the note was written on an air sickness bag.

United Airlines said in a statement that Flight 840 turned around 90 minutes into the flight. The Boeing 747 taxied to a remote spot at the airport after landing.

"As a precaution, the captain immediately returned to Sydney, landing without incident at 5:50 p.m. Further investigations will be carried out," it said.

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Flights in and out of Sydney were briefly halted or diverted while the threat was investigated, Anderson said.

"The first point to make is everyone is safe, and flights in Australia are now resuming," he added. "Things are returning to normal."

Anderson said the plane was being searched, but no bomb was immediately found. Later he told ABC television he was "pretty sure it was a hoax."

Police commander Peter O'Brien said all passengers were interviewed and released.

The flight was rescheduled to fly to Los Angeles on Wednesday.

After hearing about the emergency on the radio, Elaine Sander rushed back to the airport to meet her 18-year-old American niece Alissa Hornyak, who had been returning home after a two-week vacation in Australia.

"We haven't heard anything from the airline, and we are just waiting as you are," she said. "We are just hoping for the best."