Sydney - An audacious break-out attempt Sunday at a high-security facility in Australia saw a 27-year-old female orang-utan called Karta disable an electric fence and use a makeshift ladder for her escape, before aborting the attempt.

   Adelaide Zoo curator Peter Whitehead said Karta had used a stick to short-circuit the electric fence and piled up branches and other objects in her pen to climb to within metres of visitors.

   "You're talking about an animal that's highly intelligent," Whitehead told reporters. "We've had issues with her before in normal day-to-day operations where she tries to outsmart the keepers."

   The 62-kilogram Karta came so close to escaping her enclosure that visitors had to be ushered out and the zoo closed until she was returned to captivity.

   Veterinary staff armed with tranquilizer guns were at the ready but Karta aborted the escape herself.

   "I think when she actually got out and realized where she was ... she's realized she shouldn't be there, so then she actually hung onto the wall and dropped back into the exhibit," Whitehead said. "She's an ingenious animal."