WASHINGTON - An official of the Cincinnati Zoo denied on Monday that their management had a negligence in safety and insisted the one-meter barrier around the gorilla enclosure meets all the industry standards.

"The barriers are safe. The barriers exceed any required protocols," Thane Mayard, director of the Cincinnati Zoo and Botanical Gardens, said at a news conference about an incident that led to the death of a gorilla.

On Saturday, a 4-year-old boy climbed the barrier and through the bushes, and reached the moat filled with water surrounding the gorilla enclosure. A 17-year-old western lowland silverback gorilla, named Harambe, grabbed the boy and dragged him for meters, according to a video footage.

To rescue the boy from the hands of the agitated gorilla, zookeepers shot the animal dead although the endangered species only has a population fewer than 175,000 in the wild.

"The zoo is not negligent," Mayard insisted, adding that they will reassure the safety of the barriers.

About 20 of animal lovers staged a vigil outside the zoo, protesting the shooting. Meanwhile, more than 200,000 people signed online petitions, showing sympathy for the gorilla.

The zoo director emphasized that the decision to kill the gorilla is the right choice under that circumstance, adding that the disoriented animal was about six times stronger than a man and it was hurting the boy.

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

Many of the animal lovers blamed the boy's parents for their son's dangerous situation and the animal's death.

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

The family issued a statement to US media offering their "heartfelt thanks" to the zoo and condolence for the animal's death on Sunday.