CINCINNATI, Ohio (REUTERS) - No criminal charges will be filed against the mother of the three-year-old boy who fell into a gorilla enclosure at the Cincinnati Zoo, causing zookeepers to kill an endangered gorilla to protect the child, an Ohio prosecutor said on Monday.

A 17-year-old endangered western lowland silverback gorilla named Harambe was shot by zoo staff in the minutes after the boy fell on May 28, touching off a storm of criticism aimed at both the zoo and the boy's mother.

Some critics had called for criminal charges against the mother, who was with the boy at the zoo, for reckless endangerment. The boy suffered a concussion and some scrapes but escaped serious injury.

"I am very sorry about the loss of this gorilla but nothing about this situation rises to the level of a criminal charge," Hamilton County prosecutor Joseph Deters said on Monday.

"Had she been in the bathroom smoking crack and let her kids run around the zoo that'd be a different story," he told reporters on Monday. "She was attending to her children by all witness accounts and the three-year-old just scampered off."

He said the mother, according to witnesses, never placed her son in danger and only turned away for a few seconds to deal with another child.

"If anyone doesn't believe a three-year-old can scamper off very quickly, they've never had kids because they can and they do,"he added.

Deters also said he was glad the zoo had changed the gorilla enclosure to prevent a repeat of the incident. It will reopen on Tuesday (June 7) with a higher barrier and added knotted rope netting.

The family was pleased with the prosecutor's decision.

"This is one more step in allowing us to put this tragic episode behind us and return to our normal family life," the family said in a statement.

The boy was at the zoo with his mother, three sisters, aged seven, four and one, and family friends when he climbed over a 1m barrier and fell 4.5m into a moat, according to the Hamilton County prosecutor's office and witnesses.

The gorilla dragged the child through the enclosure. Fearing for the boy's safety, the zoo's Dangerous Animal Response Team shot and killed the gorilla, who was with the boy for 10 minutes.

The child was between the gorilla's legs when the animal was killed by a single rifle shot to the head, the prosecutor's office said.