CINCINNATI, May 30 (Reuters) - The director of the Cincinnati Zoo insisted on Monday that a three-foot (one-meter) barrier around the gorilla enclosure was adequate, even though a 4-year-old boy was able to climb over it and fall in, forcing zookeepers to shoot the ape dead after it grabbed him and dragged him around.

The death of the gorilla, a 17-year-old Western lowland silverback named Harambe, outraged animal lovers, about 20 of whom staged a vigil outside the zoo. More than 200,000 people signed online petitions on Change.org to protest the shooting, some demanding "Justice for Harambe" and urging police to hold the child's parents accountable.

"The barriers are safe. The barriers exceed any required protocols," Thane Maynard, director of the Cincinnati Zoo & Botanical Gardens, said in answer to questions at a news conference about the incident on Saturday. "The trouble with barriers is that whatever the barrier some people can get past it. ... No, the zoo is not negligent," he said.

Maynard, director of the Cincinnati Zoo & Botanical Gardens, stood by the decision to shoot the gorilla after he dragged the boy around by the ankle. He said the ape was not simply endangering the child but actually hurting him.

"Looking back, we would make the same decision," he said.

"The gorilla was clearly agitated. The gorilla was clearly disoriented," said Maynard, while lamenting the loss of "an incredibly magnificent animal."

The zoo received thousands of messages of sympathy and support from around the world, he said.

Still, Maynard faced a series of questions about how a 4-year-old was able to climb the barrier and through the bushes and reach the 15-foot drop into the water surrounding the enclosure.

The exhibit met standards set by the Association of Zoos and Aquariums (AZA) and U.S. Department of Agriculture (USDA), which conduct regular inspections, Maynard said.

He said zookeepers would review the barrier but he made no promise to redesign it.

The zoo association's 2016 accreditation standards, published on its website, said "some means of deterring public contact with animals (e.g., guardrails/barriers) must be in place."

"Insufficient barrier fencing" is listed as one risk to visitors.

Animal lovers turned their anger toward the parents while mourning the death of the gorilla, lighting candles and holding "Rest in Peace" signs at the vigil.

"That child's life was in danger. At the end of the day, it falls on the parents. No one else," said Vanessa Hammonds, 27, who said she flew in from Houston to attend the vigil.

Authorities have not identified the boy. Michelle Gregg, who identified herself on Facebook as his mother, asked others not to judge her because "accidents happen." She said her son was recovering from a concussion and a few scrapes.

A family statement on Sunday expressed condolences for the animal's death.

"We extend our heartfelt thanks for the quick action by the Cincinnati Zoo staff," the statement said. "We know that this was a very difficult decision for them, and that they are grieving the loss of their gorilla." (Reporting by Ginny McCabe, Barbara Goldberg and Ian Simpson; Editing by Daniel Trotta and David Gregorio)