HOUSTON —  A note found in a Southwest Airlines (search) seat pocket claiming a bomb was on the plane prompted a landing and evacuation on an isolated stretch of runway Friday, but bomb-sniffing dogs found no signs of explosives, authorities said.

Investigators interviewed and re-screened the 136 passengers who had been on the flight from Dallas to Houston.

Three passengers who saw the note were still being interviewed late Friday afternoon, but no one had been taken into custody, FBI (search) spokesman Al Tribble said.

Tribble said he didn't have the exact wording of the note, but "it definitely announced there's a bomb on the plane."

A passenger alerted crew members to the note while the plane was in the air, saying it had been found in a seat pocket. It was unclear whether the note was written on that flight or had been left during a previous flight, Tribble said.

No one was injured, and bomb-sniffing dogs found no evidence of explosives on the plane after the search, said Andrea McCauley, spokeswoman with the Transportation Security Administration (search).

Hobby Airport (search), where the plane landed, is the smaller of Houston's two major airports, handling only domestic flights.

Police, fire and medical crews had been sent to the landing site as a precaution.